diff --git a/library/Zend/Pdf/Resource/Font/Simple.php b/library/Zend/Pdf/Resource/Font/Simple.php
index 63a5258115..a7ae546950 100644
--- a/library/Zend/Pdf/Resource/Font/Simple.php
+++ b/library/Zend/Pdf/Resource/Font/Simple.php
@@ -173,6 +173,10 @@ public function glyphNumberForCharacter($characterCode)
      */
     public function getCoveredPercentage($string, $charEncoding = '')
     {
+        if ($string === null || $string === '') {
+            return 0;
+        }
+
         /* Convert the string to UTF-16BE encoding so we can match the string's
          * character codes to those found in the cmap.
          */
@@ -261,6 +265,10 @@ public function widthForGlyph($glyphNumber)
      */
     public function encodeString($string, $charEncoding)
     {
+        if ($string === null || $string === '') {
+            return '';
+        }
+
         if (PHP_OS == 'AIX') {
             return $string; // returning here b/c AIX doesnt know what CP1252 is
         }
@@ -279,6 +287,10 @@ public function encodeString($string, $charEncoding)
      */
     public function decodeString($string, $charEncoding)
     {
+        if ($string === null || $string === '') {
+            return '';
+        }
+
         return iconv('CP1252', $charEncoding, $string);
     }
 }