diff --git a/src/Converter/Conversion.php b/src/Converter/Conversion.php
index 2ea8a23..a10fa09 100644
--- a/src/Converter/Conversion.php
+++ b/src/Converter/Conversion.php
@@ -76,7 +76,7 @@ public function getTo()
      *
      * @param DateRepresentationInterface $to the to
      *
-     * @return self|null
+     * @return self
      */
     public function setTo(DateRepresentationInterface $to)
     {
@@ -92,7 +92,7 @@ public function setTo(DateRepresentationInterface $to)
      */
     public function getUnixTime()
     {
-        return $this->unixTime;
+        return (int)$this->unixTime;
     }
 
     /**
diff --git a/src/Converter/UnixTimeConverter/Date.php b/src/Converter/UnixTimeConverter/Date.php
index 9248007..4b65ac2 100644
--- a/src/Converter/UnixTimeConverter/Date.php
+++ b/src/Converter/UnixTimeConverter/Date.php
@@ -24,13 +24,9 @@ class Date implements UnixTimeConverterInterface
      */
     public function fromUnixTime(Conversion $conversion)
     {
-        if (null === $res = $conversion->getTo()) {
-            return;
-        }
-
         $from = $conversion->getFrom();
 
-        $res = $res
+        $res = $conversion->getTo()
             ->withUnixTime($from->getUnixTime())
             ->withUnixMicroTime($from->getUnixMicroTime())
             ->withTimezone($from->getTimezone())
diff --git a/src/Converter/UnixTimeConverter/DateSolar.php b/src/Converter/UnixTimeConverter/DateSolar.php
index a2c14d4..285ca50 100644
--- a/src/Converter/UnixTimeConverter/DateSolar.php
+++ b/src/Converter/UnixTimeConverter/DateSolar.php
@@ -2,7 +2,6 @@
 
 namespace Popy\Calendar\Converter\UnixTimeConverter;
 
-use BCMathExtended\BC;
 use Popy\Calendar\Converter\Conversion;
 use Popy\Calendar\Converter\UnixTimeConverterInterface;
 use Popy\Calendar\Converter\CompleteLeapYearCalculatorInterface;
@@ -68,7 +67,7 @@ public function fromUnixTime(Conversion $conversion)
         // TODO : remove code repetition by using a separate abstraction
         // handling basic math operations.
 
-        if (is_integer($this->dayLengthInSeconds) || !class_exists(BC::class)) {
+        if (is_integer($this->dayLengthInSeconds)) {
             // bc not needed/not available
 
             // Relative time from era start.
@@ -95,12 +94,12 @@ public function fromUnixTime(Conversion $conversion)
 
             // Calculating global day index. Floor is used to properly handle
             // negative values
-            $eraDayIndex = BC::floor(
+            $eraDayIndex = floor(
                 bcdiv($relativeTime, $this->dayLengthInSeconds)
             );
 
             // TODO : handle the loss as microseconds ?
-            $time = BC::ceil(bcsub(
+            $time = ceil(bcsub(
                 $relativeTime,
                 bcmul($eraDayIndex, $this->dayLengthInSeconds)
             ));
@@ -131,7 +130,7 @@ public function toUnixTime(Conversion $conversion)
             return;
         }
 
-        $year = $input->getYear();
+        $year = (int)$input->getYear();
         $eraDayIndex = $input->getDayIndex()
             + $this->calculator->getYearEraDayIndex($year)
         ;
diff --git a/src/Converter/UnixTimeConverter/Iso8601Weeks.php b/src/Converter/UnixTimeConverter/Iso8601Weeks.php
index c5f09f5..87e693f 100644
--- a/src/Converter/UnixTimeConverter/Iso8601Weeks.php
+++ b/src/Converter/UnixTimeConverter/Iso8601Weeks.php
@@ -56,7 +56,7 @@ public function fromUnixTime(Conversion $conversion)
             return;
         }
 
-        $year = $input->getYear();
+        $year = (int)$input->getYear();
         // Assuming the era starting year is 1970, it starts a Thursday.
         $dayOfWeek = ($input->getEraDayIndex() + $this->firstYearDayIndex) % 7;
 
diff --git a/src/Converter/UnixTimeConverter/TimeOffset.php b/src/Converter/UnixTimeConverter/TimeOffset.php
index f063032..7e83313 100644
--- a/src/Converter/UnixTimeConverter/TimeOffset.php
+++ b/src/Converter/UnixTimeConverter/TimeOffset.php
@@ -32,11 +32,9 @@ public function fromUnixTime(Conversion $conversion)
             $conversion->getUnixTime() + $offset->getValue()
         );
 
-        if (null !== $conversion->getTo()) {
-            $conversion->setTo(
-                $conversion->getTo()->withOffset($offset)
-            );
-        }
+        $conversion->setTo(
+            $conversion->getTo()->withOffset($offset)
+        );
     }
 
     /**
diff --git a/src/Factory/ConfigurableFactory.php b/src/Factory/ConfigurableFactory.php
index a85473a..a71aeb9 100644
--- a/src/Factory/ConfigurableFactory.php
+++ b/src/Factory/ConfigurableFactory.php
@@ -82,7 +82,7 @@ class ConfigurableFactory
     /**
      * Available values for option "additional_symbol_parser"
      *
-     * @var array<string>
+     * @var array<string|boolean>
      */
     protected $additional_symbol_parser = [
         'none'    => false,
@@ -135,8 +135,8 @@ public function buildConverter(array $options = array())
     /**
      * Generic service getter.
      *
-     * @param string $service  Service name.
-     * @param array  &$options Option array
+     * @param string $service Service name.
+     * @param array  $options Option array
      *
      * @return mixed
      */
diff --git a/src/Formatter/AgnosticFormatter.php b/src/Formatter/AgnosticFormatter.php
index b2ea6f2..3de0dc6 100644
--- a/src/Formatter/AgnosticFormatter.php
+++ b/src/Formatter/AgnosticFormatter.php
@@ -56,9 +56,7 @@ public function format(DateTimeInterface $input, $format)
     {
         $date = Date::buildFromDateTimeInterface($input);
 
-        if (null === $date = $this->converter->to($date)) {
-            return;
-        }
+        $date = $this->converter->to($date);
 
         return $this->formatDateRepresentation($date, $format);
     }
diff --git a/src/Formatter/NumberConverter/RFC2550.php b/src/Formatter/NumberConverter/RFC2550.php
index 9ced7d7..2b21aec 100644
--- a/src/Formatter/NumberConverter/RFC2550.php
+++ b/src/Formatter/NumberConverter/RFC2550.php
@@ -103,7 +103,7 @@ public function from($input)
      *
      * @param string $input
      *
-     * @return string
+     * @return string|null
      */
     public function convertFromPositive($input)
     {
@@ -117,7 +117,7 @@ public function convertFromPositive($input)
                 $matches
             )
         ) {
-            return;
+            return null;
         }
 
         if ($matches['alpha'] === '') {
@@ -148,7 +148,7 @@ public function convertFromPositive($input)
      *
      * @param string $input
      *
-     * @return string
+     * @return string|null
      */
     public function convertFromNegative($input)
     {
diff --git a/src/Formatter/SymbolFormatter/StandardDateFragmented.php b/src/Formatter/SymbolFormatter/StandardDateFragmented.php
index d0ed68f..acba1d1 100644
--- a/src/Formatter/SymbolFormatter/StandardDateFragmented.php
+++ b/src/Formatter/SymbolFormatter/StandardDateFragmented.php
@@ -44,12 +44,16 @@ public function formatSymbol(DateRepresentationInterface $input, FormatToken $to
 
         if ($token->is('F')) {
             // F   A full textual representation of a month
-            return (string)$this->locale->getMonthName($input->getDateParts()->get(0));
+            return (string)$this->locale->getMonthName(
+                $input->getDateParts()->get(0)
+            );
         }
 
         if ($token->is('M')) {
             // M   A short textual representation of a month, three letters
-            return (string)$this->locale->getMonthShortName($input->getDateParts()->get(0));
+            return (string)$this->locale->getMonthShortName(
+                $input->getDateParts()->get(0)
+            );
         }
 
         if ($token->is('m')) {
@@ -79,17 +83,23 @@ public function formatSymbol(DateRepresentationInterface $input, FormatToken $to
 
         if ($token->is('S')) {
             // S   English ordinal suffix for the day of the month, 2 characters
-            return (string)$this->locale->getNumberOrdinalSuffix($input->getDateParts()->get(1));
+            return $this->locale->getNumberOrdinalSuffix(
+                (int)$input->getDateParts()->get(1)
+            );
         }
 
         if ($token->is('l')) {
             // l (lowercase 'L')   A full textual representation of the day of the week
-            return (string)$this->locale->getDayName($input->getDateParts()->getTransversal(2));
+            return (string)$this->locale->getDayName(
+                $input->getDateParts()->getTransversal(2)
+            );
         }
 
         if ($token->is('D')) {
             // D   A textual representation of a day, three letters
-            return (string)$this->locale->getDayShortName($input->getDateParts()->getTransversal(2));
+            return (string)$this->locale->getDayShortName(
+                $input->getDateParts()->getTransversal(2)
+            );
         }
         
         if ($token->is('w')) {
diff --git a/src/Formatter/SymbolFormatter/StandardDateSolar.php b/src/Formatter/SymbolFormatter/StandardDateSolar.php
index 2b4d210..de6f905 100644
--- a/src/Formatter/SymbolFormatter/StandardDateSolar.php
+++ b/src/Formatter/SymbolFormatter/StandardDateSolar.php
@@ -41,7 +41,7 @@ public function formatSymbol(DateRepresentationInterface $input, FormatToken $to
         }
         if ($token->is('y')) {
             // y   A two digit representation of a year
-            return $this->converter->to($input->getYear());
+            return $this->converter->to($input->getYear() ?: 0);
         }
 
         if ($token->is('Y')) {
diff --git a/src/Parser/AgnosticParser.php b/src/Parser/AgnosticParser.php
index a6b863e..bdae84c 100644
--- a/src/Parser/AgnosticParser.php
+++ b/src/Parser/AgnosticParser.php
@@ -85,20 +85,18 @@ public function parse($input, $format, DateTimeZone $timezone = null)
      */
     public function parseToDateRepresentation($input, $format, DateTimeZone $timezone = null)
     {
-        if (null === $lexer = $this->parser->parseFormat($format)) {
-            return;
-        }
+        $lexer = $this->parser->parseFormat($format);
 
         if (null === $parts = $lexer->tokenizeDate($input)) {
-            return;
+            return null;
         }
 
         $date = Date::buildFromTimezone($timezone);
 
         if (null === $date = $this->mapper->map($parts, $date)) {
-            return;
+            return null;
         }
 
-        return $date;
+        return $this->mapper->map($parts, $date);
     }
 }
diff --git a/src/Parser/DateLexer/PregChoice.php b/src/Parser/DateLexer/PregChoice.php
index 15982ed..1fc4f2d 100644
--- a/src/Parser/DateLexer/PregChoice.php
+++ b/src/Parser/DateLexer/PregChoice.php
@@ -65,25 +65,30 @@ public function hydrateResult(DateLexerResult $result, $match, $offset = 1)
             return $offset;
         }
 
+        if (
+            null === $this->symbol // nothing to map
+            || $match[$offset][1] === -1 // didn't match
+        ) {
+            return $offset + 1;
+        }
+
         // Did match
-        if ($match[$offset][1] !== -1) {
-            $found = array_search($match[$offset][0], $this->choices);
-
-            // DO THE MAGIC
-            if ($found === false) {
-                $res = preg_grep(
-                    '/^' . preg_quote($match[$offset][0], '/') . '$/i',
-                    $this->choices
-                );
-
-                if (count($res)) {
-                    reset($res);
-                    $found = key($res);
-                }
+        $found = array_search($match[$offset][0], $this->choices);
+
+        // DO THE MAGIC
+        if ($found === false) {
+            $res = preg_grep(
+                '/^' . preg_quote($match[$offset][0], '/') . '$/i',
+                $this->choices
+            );
+
+            if (count($res)) {
+                reset($res);
+                $found = key($res);
             }
-            
-            $result->set($this->symbol, $found);
         }
+        
+        $result->set($this->symbol, $found);
 
         return $offset + 1;
     }
diff --git a/src/Parser/FormatParser/Basic.php b/src/Parser/FormatParser/Basic.php
index 8b2247f..f7dffcd 100644
--- a/src/Parser/FormatParser/Basic.php
+++ b/src/Parser/FormatParser/Basic.php
@@ -3,11 +3,9 @@
 namespace Popy\Calendar\Parser\FormatParser;
 
 use Popy\Calendar\Parser\FormatLexerInterface;
-use Popy\Calendar\Parser\FormatLexer\MbString;
 use Popy\Calendar\Parser\SymbolParserInterface;
 use Popy\Calendar\Parser\FormatParserInterface;
 use Popy\Calendar\Parser\DateLexer\Collection;
-use Popy\Calendar\Parser\SymbolParser\PregNative;
 use Popy\Calendar\Parser\DateLexer\NonSymbolMatcher;
 
 /**
@@ -37,13 +35,13 @@ class Basic implements FormatParserInterface
     /**
      * Class constructor.
      *
-     * @param FormatLexerInterface|null  $lexer        Format lexer.
-     * @param SymbolParserInterface|null $symbolParser Symbol Parser
+     * @param FormatLexerInterface  $lexer        Format lexer.
+     * @param SymbolParserInterface $symbolParser Symbol Parser
      */
-    public function __construct(FormatLexerInterface $lexer = null, SymbolParserInterface $symbolParser = null)
+    public function __construct(FormatLexerInterface $lexer, SymbolParserInterface $symbolParser)
     {
-        $this->lexer = $lexer ?: new MbString();
-        $this->symbolParser = $symbolParser ?: new PregNative();
+        $this->lexer = $lexer;
+        $this->symbolParser = $symbolParser;
     }
 
 
diff --git a/src/Parser/FormatParser/PregExtendedNative.php b/src/Parser/FormatParser/PregExtendedNative.php
index c135204..d7b2785 100644
--- a/src/Parser/FormatParser/PregExtendedNative.php
+++ b/src/Parser/FormatParser/PregExtendedNative.php
@@ -4,12 +4,10 @@
 
 use Popy\Calendar\Parser\FormatToken;
 use Popy\Calendar\Parser\FormatLexerInterface;
-use Popy\Calendar\Parser\FormatLexer\MbString;
 use Popy\Calendar\Parser\FormatParserInterface;
 use Popy\Calendar\Parser\SymbolParserInterface;
 use Popy\Calendar\Parser\DateLexer\PregSimple;
 use Popy\Calendar\Parser\DateLexer\PregCollection;
-use Popy\Calendar\Parser\SymbolParser\PregNative;
 
 /**
  * Preg based implementation of the native DateTimeInterface format, with an
@@ -39,13 +37,13 @@ class PregExtendedNative implements FormatParserInterface
     /**
      * Class constructor.
      *
-     * @param FormatLexerInterface|null  $lexer        Format lexer.
-     * @param SymbolParserInterface|null $symbolParser Symbol Parser
+     * @param FormatLexerInterface  $lexer        Format lexer.
+     * @param SymbolParserInterface $symbolParser Symbol Parser
      */
-    public function __construct(FormatLexerInterface $lexer = null, SymbolParserInterface $symbolParser = null)
+    public function __construct(FormatLexerInterface $lexer, SymbolParserInterface $symbolParser)
     {
-        $this->lexer = $lexer ?: new MbString();
-        $this->symbolParser = $symbolParser ?: new PregNative();
+        $this->lexer = $lexer;
+        $this->symbolParser = $symbolParser;
     }
 
     /**
diff --git a/src/Parser/FormatToken.php b/src/Parser/FormatToken.php
index 16d4d7a..8404b93 100644
--- a/src/Parser/FormatToken.php
+++ b/src/Parser/FormatToken.php
@@ -48,7 +48,7 @@ public function __construct($value, $type)
     /**
      * Gets the token value.
      *
-     * @return string
+     * @return string|null
      */
     public function getValue()
     {
@@ -58,7 +58,7 @@ public function getValue()
     /**
      * Gets the token name (possibly aliased).
      *
-     * @return string
+     * @return string|null
      */
     public function getName()
     {
@@ -97,7 +97,7 @@ public function is($symbol)
      * or one of the symbol contained in the first argument if it is an array
      *
      * @param array|string $symbols
-     * @param string       ...$symbol
+     * @param string       ...$symbols
      *
      * @return boolean
      */
diff --git a/src/Parser/ResultMapper/StandardDate.php b/src/Parser/ResultMapper/StandardDate.php
index 113f271..0e6ed68 100644
--- a/src/Parser/ResultMapper/StandardDate.php
+++ b/src/Parser/ResultMapper/StandardDate.php
@@ -90,13 +90,13 @@ protected function determineOffset(DateLexerResult $parts, TimeOffset $offset)
      * Determine date's timezone. If an offset has been found, Timezone has
      * no effect on the date parsing, but will have on the date display.
      *
-     * @param DateLexerResult $parts   Date lexer results.
-     * @param integer|null    $offset  Date offset if it has been found.
-     * @param DateTimeZone    $inputTz Default timezone if any.
+     * @param DateLexerResult   $parts   Date lexer results.
+     * @param TimeOffset        $offset  Date offset.
+     * @param DateTimeZone|null $inputTz Default timezone if any.
      *
      * @return DateTimeZone
      */
-    protected function determineTimezone(DateLexerResult $parts, TimeOffset $offset, DateTimeZone $inputTz)
+    protected function determineTimezone(DateLexerResult $parts, TimeOffset $offset, DateTimeZone $inputTz = null)
     {
         // e   Timezone identifier (added in PHP 5.1.0)    Examples: UTC, GMT, Atlantic/Azores
         // O   Difference to Greenwich time (GMT) in hours Example: +0200
diff --git a/src/Parser/ResultMapper/StandardDateFragmented.php b/src/Parser/ResultMapper/StandardDateFragmented.php
index 8526327..890a5a3 100644
--- a/src/Parser/ResultMapper/StandardDateFragmented.php
+++ b/src/Parser/ResultMapper/StandardDateFragmented.php
@@ -112,7 +112,7 @@ protected function determineDayOfWeek(DateLexerResult $parts)
     protected function determineWeekIndex(DateLexerResult $parts)
     {
         if (null === $w = $parts->get('W')) {
-            return;
+            return null;
         }
 
         return intval($w) - 1;
diff --git a/src/Parser/SymbolParser/PregNativeDateFragmented.php b/src/Parser/SymbolParser/PregNativeDateFragmented.php
index 0eebd59..86870f3 100644
--- a/src/Parser/SymbolParser/PregNativeDateFragmented.php
+++ b/src/Parser/SymbolParser/PregNativeDateFragmented.php
@@ -147,7 +147,7 @@ protected function buildSuffixesLexer(FormatToken $token)
         $i = 0;
         $repetitions = 0;
 
-        while (null !== $label = $this->locale->getNumberOrdinalSuffix($i++)) {
+        while ($label = $this->locale->getNumberOrdinalSuffix($i++)) {
             if (!in_array($label, $choices)) {
                 $choices[] = $label;
                 $repetitions = 0;
diff --git a/src/PresetParser.php b/src/PresetParser.php
index 7fcf9c8..58eb25d 100644
--- a/src/PresetParser.php
+++ b/src/PresetParser.php
@@ -40,7 +40,7 @@ public function __construct(ParserInterface $parser, $format)
      *
      * @param string $input
      *
-     * @return DateTimeInterface
+     * @return DateTimeInterface|null
      */
     public function parse($input)
     {
diff --git a/src/ValueObject/AbstractFragmentedDuration.php b/src/ValueObject/AbstractFragmentedDuration.php
index f2861ea..8cd7603 100644
--- a/src/ValueObject/AbstractFragmentedDuration.php
+++ b/src/ValueObject/AbstractFragmentedDuration.php
@@ -254,17 +254,18 @@ public function withTransversals(array $transversals)
     /**
      * Ensure each consecutive key of the input array is set (filling with nulls)
      *
-     * @param array<integer|null> $input
+     * @param array<mixed|null> $input
+     * @param mixed             $default Filling value.
      *
-     * @return array<integer|null>
+     * @return array<mixed|null>
      */
-    protected function fillArrayInput(array $input)
+    protected function fillArrayInput(array $input, $default = 0)
     {
         if (empty($input)) {
             return [];
         }
 
-        $res = array_fill(0, max(array_keys($input)), null);
+        $res = array_fill($default, max(array_keys($input)), null);
 
         foreach ($input as $index => $value) {
             $res[$index] = $value;
diff --git a/src/ValueObject/DateRepresentation/Date.php b/src/ValueObject/DateRepresentation/Date.php
index 4b32b0e..5eda25d 100644
--- a/src/ValueObject/DateRepresentation/Date.php
+++ b/src/ValueObject/DateRepresentation/Date.php
@@ -30,7 +30,7 @@ class Date implements DateRepresentationInterface
     /**
      * Timezone.
      *
-     * @var DateTimeZone
+     * @var DateTimeZone|null
      */
     protected $timezone;
 
diff --git a/src/ValueObject/Time.php b/src/ValueObject/Time.php
index 3a3ee97..661d694 100644
--- a/src/ValueObject/Time.php
+++ b/src/ValueObject/Time.php
@@ -54,7 +54,7 @@ public function __construct(array $fragments = [], array $sizes = [], $ratio = n
     public function get($i)
     {
         if (!isset($this->fragments[$i])) {
-            return;
+            return null;
         }
 
         if (
@@ -89,13 +89,14 @@ public function get($i)
      *
      * @param integer $i Fragment index
      *
-     * @return integer
+     * @return integer|null
      */
     public function getHalved($i)
     {
         if (!isset($this->fragments[$i])) {
-            return;
+            return null;
         }
+
         if (!isset($this->sizes[$i])) {
             return $this->fragments[$i];
         }
@@ -115,7 +116,7 @@ public function canBeHalved($i)
             !isset($this->fragments[$i])
             || !isset($this->sizes[$i])
         ) {
-            return;
+            return null;
         }
 
         $half = (int)floor($this->sizes[$i] / 2);
@@ -198,7 +199,7 @@ public function withHalveds(array $halved)
     {
         $res = clone $this;
 
-        $this->halved = $this->fillArrayInput($halved);
+        $this->halved = $this->fillArrayInput($halved, false);
 
         return $res;
     }