Add NoneMatcher.

matcher/src/main/java/com/pressassociation/pr/match/Matcher.java

@@ -54,6 +54,13 @@ public static Matcher all() {
     return AllMatcher.INSTANCE;
   }
 
+  /**
+   * Return a Matcher that will <em>not</em> match any path. Equivalent to {@code Matchers.of("")}.
+   */
+  public static Matcher none() {
+    return NoneMatcher.INSTANCE;
+  }
+
   /**
    * Get a new Matcher that will match against the given fields string. The string should be a valid fields string,
    * something like {@code items/name(type,value)}.
@@ -66,6 +73,9 @@ public static Matcher of(CharSequence fields) {
     if ("*".equals(fields)) {
       return all();
     }
+    if (fields.toString().isEmpty()) {
+      return none();
+    }
     return new AstMatcher(new Parser().parse(checkNotNull(fields)));
   }
 

matcher/src/main/java/com/pressassociation/pr/match/NoneMatcher.java

@@ -0,0 +1,60 @@
+/*
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2014 Press Association Limited
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+package com.pressassociation.pr.match;
+
+/**
+ * Matcher implementation that doesn't match anything.
+ *
+ * @author Matt Nathan
+ */
+class NoneMatcher extends Matcher {
+
+  static final Matcher INSTANCE = new NoneMatcher();
+
+  @Override
+  public boolean matches(Leaf leaf) {
+    return false;
+  }
+
+  @Override
+  public boolean matchesAll() {
+    return false;
+  }
+
+  @Override
+  public boolean matchesParent(Leaf node) {
+    return false;
+  }
+
+  @Override
+  protected String patternString() {
+    return "";
+  }
+
+  @Override
+  public String toString() {
+    return "Matcher.none()";
+  }
+}

matcher/src/test/java/com/pressassociation/pr/match/MatcherTest.java

@@ -67,12 +67,29 @@ public void testReadmeExamples() {
     assertFalse(matcher.matches("/spouse/children"));
   }
 
+  @Test
+  public void testEmptyIsNone() {
+    assertSame(Matcher.none(), Matcher.of(""));
+  }
+
   @Test
   public void testMatchesAll() {
     assertTrue(Matcher.of("*").matchesAll());
     assertTrue(Matcher.all().matchesAll());
     assertFalse(Matcher.of("all").matchesAll());
     assertFalse(Matcher.of("all/*").matchesAll());
+    assertFalse(Matcher.of("").matchesAll());
+    assertFalse(Matcher.none().matchesAll());
+  }
+
+  @Test
+  @Parameters({
+      "a",
+      "a/b",
+      "foo/bar/baz"
+  })
+  public void testNoneMatchesNothing(CharSequence path) {
+    assertFalse(Matcher.none().matches(path));
   }
 
   @Test
@@ -122,6 +139,16 @@ public void testMatchesParentAll() {
     assertTrue(Matcher.all().matchesParent("my/node/continues"));
   }
 
+  @Test
+  @Parameters({
+      "a",
+      "a/b",
+      "foo/bar/baz"
+  })
+  public void testNoneMatchesNothingParent(CharSequence path) {
+    assertFalse(Matcher.none().matchesParent(path));
+  }
+
   @Test
   public void testTransform() {
     assertEquals("*", Matcher.all().transform(Functions.constant("foo")).patternString());