title: assertEquals Fails when I'm returning null
body: <p>I'm trying to implement Mockito to test a particular method but the .thenReturn(null) seems not returning null value.</p>
  
  <pre><code>@RunWith(PowerMockRunner.class)
  @PrepareForTest({ ValidationServiceImpl.class})
  public class ValidationServiceTest {
  
      @Test
      public void testGetProdList() throws Exception{
          IValidationDao validationDao = Mockito.mock(ValidationDaoImpl.class);
          IValidationService validationService = Mockito.mock(ValidationServiceImpl.class);
          ReflectionTestUtils.setField(validationService, "validationDao", validationDao);
          List&lt;ProductDetailsBean&gt; prodGroups = new  ArrayList&lt;ProductDetailsBean&gt;();
          for (int i = 0; i &lt; 145; i++) 
              prodGroups.add(new ProductDetailsBean());
          Mockito.when(validationDao.getProdList(12345)).thenReturn(prodGroups);
          assertNotEquals(null, validationService.getProdList(12345));
      }
  
      @Test
      public void testGetProdListwithNullTest() throws Exception{
          IValidationDao validationDao = Mockito.mock(ValidationDaoImpl.class);
          IValidationService validationService = Mockito.mock(ValidationServiceImpl.class);
          ReflectionTestUtils.setField(validationService, "validationDao", validationDao);
          Mockito.when(validationDao.getProdList(11111)).thenReturn(null);
          assertEquals(null, validationService.getProdList(11111));
      }   
  }
  </code></pre>
  
  <p>My first test case is working fine second one is failing..</p>
  
  <p>Stack trace:</p>
  
  <pre><code>java.lang.AssertionError: expected:&lt;null&gt; but was:&lt;[]&gt;
      at org.junit.Assert.fail(Assert.java:88)
      at org.junit.Assert.failNotEquals(Assert.java:743)
      at org.junit.Assert.assertEquals(Assert.java:118)
      at org.junit.Assert.assertEquals(Assert.java:144)
      at uk.co.argos.pst.test.sevices.ValidationServiceTest.testGetProdListwithNullTest(ValidationServiceTest.java:53)
  </code></pre>
  
  <p>Please help me where I'm doing wrong.</p>