Fixed issue #77: NullPointerException on null unsafe Comparable implementations

Author: SQiShER

src/main/java/de/danielbechler/util/Comparables.java

@@ -25,14 +25,14 @@ private Comparables()
 
 	public static <T extends Comparable<T>> boolean isEqualByComparison(final T a, final T b)
 	{
-		if (a != null)
+		if (a == null && b == null)
 		{
-			return a.compareTo(b) == 0;
+			return true;
 		}
-		else if (b != null)
+		else if (a != null && b != null)
 		{
-			return b.compareTo(a) == 0;
+			return a.compareTo(b) == 0;
 		}
-		return true;
+		return false;
 	}
 }

src/test/java/de/danielbechler/diff/integration/issues/Issue77Test.groovy

@@ -0,0 +1,52 @@
+/*
+ * Copyright 2013 Daniel Bechler
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package de.danielbechler.diff.integration.issues
+
+import de.danielbechler.diff.ObjectDifferFactory
+import spock.lang.Specification
+
+/**
+ * @author Daniel Bechler
+ */
+class Issue77Test extends Specification
+{
+  def "NullPointerException on null unsafe Comparable implementations"()
+  {
+    expect:
+    ObjectDifferFactory.getInstance().compare(new SomeObject(BigDecimal.ONE), new SomeObject(null));
+  }
+
+  class SomeObject
+  {
+    BigDecimal value;
+
+    SomeObject(BigDecimal value)
+    {
+      this.value = value;
+    }
+
+    BigDecimal getValue()
+    {
+      return value
+    }
+
+    void setValue(final BigDecimal value)
+    {
+      this.value = value
+    }
+  }
+}

src/test/resources/de/danielbechler/util/ComparablesSpec.groovy

@@ -0,0 +1,51 @@
+/*
+ * Copyright 2013 Daniel Bechler
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package de.danielbechler.util
+
+import spock.lang.Specification
+
+/**
+ * @author Daniel Bechler
+ */
+class ComparablesSpec extends Specification
+{
+  def "isEqualByComparison should return true when both parameters are null"()
+  {
+    expect:
+    Comparables.isEqualByComparison(null, null)
+  }
+
+  def "isEqualByComparison should return true when both arguments are equal by comparison"()
+  {
+    expect:
+    Comparables.isEqualByComparison(new BigDecimal(10), new BigDecimal(10))
+  }
+
+  def "isEqualByComparison should be null-safe even if compareTo method of comparable types is not"()
+  {
+    when:
+    def result = Comparables.isEqualByComparison(a, b)
+
+    then:
+    !result
+
+    where:
+    a              | b
+    BigDecimal.ONE | null
+    null           | BigDecimal.TEN
+  }
+}