java.lang.NullPointerException for null input in null safe static method

Question

@Test
fun isEmpty_null_true(){
    Assert.assertEquals(StringUtils.isEmpty(null),true)
}

public static boolean isEmpty(@Nullable String value) {
    return (TextUtils.isEmpty(value) || value.trim().isEmpty());
}

All test methods except above one are working and passed. I am getting java.lang.NullPointerException for this one. The implementation of StringUtils.isEmpty() is also mentioned above. StringUtils class is written in Java whereas test case file is written in Kotlin.

Answer 1

The complete solution, I have got-
Due to default values set in app/build.gradle, I was getting false returned from TextUtils.isEmpty() which was not expected by me.

testOptions {
    unitTests.returnDefaultValues = true
}

Reference - TextUtils.isEmpty(null) returns false
I cannot change the value in build.gradle file, so I needed the solution for my unit test method only. There is a way to provide implementation to TextUtils.isEmpty() method and get the real returned value.

    @Before
    public void setup() {
        PowerMockito.mockStatic(TextUtils.class);
        PowerMockito.when(TextUtils.isEmpty(any(CharSequence.class))).thenAnswer(new Answer<Boolean>() {
            @Override
            public Boolean answer(InvocationOnMock invocation) throws Throwable {
                CharSequence a = (CharSequence) invocation.getArguments()[0];
                return !(a != null && a.length() > 0);
            }
        });
   }

Reference - Need help to write a unit test using Mockito and JUnit4

I got the same problem with android.graphics.Color.parseColor() so above solution applies to all classes lies in android package.