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.

@ShaluTD cannot share complete class, it belongs to production code. Please share your query. — Harish Gyanani, Jul 11 '20 at 10:20
Why didnt you tell before? Then check for null before you call isEmpty. And you did not show code for that function so what do you expect from us? — blackapps, Jul 11 '20 at 10:25
@blackapps it is a android system method, so i didn't specify. `public static boolean isEmpty(@Nullable CharSequence str) { return str == null || str.length() == 0; }` — Harish Gyanani, Jul 11 '20 at 13:09
@AnimeshSahu `StringUtils.isEmpty` and `TextUtils.isEmpty` has only one difference, which is `trim` method. — Harish Gyanani, Jul 12 '20 at 05:13
Can you please: 1. Post entire stack trace. 2. If possible, run on JDK 14 with `-XX:+ShowCodeDetailsInExceptionMessages` 3. What is @Nullable (show fully qualified name) — Lesiak, Jul 13 '20 at 20:01
Is your question "why is this throwing a `NullPointerException`?". Or is your question "given that I know that this will throw a `NullPointerException`, how do I write a test for it?". — CommonsWare, Jul 16 '20 at 19:05
It should not throw NullPointerException due to null check written in method. I need answer to make it work. @CommonsWare — Harish Gyanani, Jul 17 '20 at 09:07

Arpan Sarkar · Answer 1 · 2020-07-13T19:11:57.620

4

The problem lies in this StringUtils.isEmpty() method itself because sometime TextUtils.isEmpty(null) returns false at that time you are passing value as null then you are invoking trim() method on the null value that is causing the java.lang.NullPointerException modify the method like this to avoid java.lang.NullPointerException

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

edited Jul 13 '20 at 19:11

answered Jul 13 '20 at 19:05

Arpan Sarkar

2,301
2
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I got your point but just to make unit test pass, I cannot change method implementation. I have seen link attached. Can you provide a way to really call TextUtils method or mock completely only for these methods. Not for all. – Harish Gyanani Jul 16 '20 at 05:46
@HarishGyanani: "I cannot change method implementation" -- you do not have a choice. Your method claims to support `null` as a value, and it does not. You could change `@Nullable` to `@NotNull` and remove the unit test, or you could rewrite the method to be `null`-safe, as in this answer. – CommonsWare Jul 17 '20 at 10:58
Change in `Nullable` to `NotNull` is also a change in code so the tests should be according to the current code as OP is only doing the testing part. – Pavneet_Singh Jul 20 '20 at 13:41

Pavneet_Singh · Answer 2 · 2020-07-16T14:13:32.673

As you know, || operator will invoke the code on both sides (to get one true value) and null.trim().. will cause the exception.

Since the expected behavior of StringUtils.isEmpty method is to throw an exception when a null value is being passed so you should write the unit test to expect an exception with null value as:

@Test(expected = NullPointerException::class)
fun isEmpty_null_exception(){
    StringUtils.isEmpty(null)
}

here excepted is used to assert that this test method throws a NullPointerException exception.

Note: Using mock for StringUtils.isEmpty static method is done with PowerMock framework but this will violate the purpose of testing to test the actual behavior of code so use the above-recommended approach to verify exception. You may want to create a mocked input variable and mock trim method but then you can simply use a non-null input string, won't be any difference.

if first condition is false then second condition is evaluated. "OR" operator works like this. — Harish Gyanani, Jul 19 '20 at 16:56
@HarishGyanani The details in this answer is specific to the current post, not general :) — Pavneet_Singh, Jul 20 '20 at 13:38

score 0 · Accepted Answer · answered Jul 18 '20 at 06:58

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.

As mentioned in [my answer](https://stackoverflow.com/a/62936560/4936904), you used the power mock approach as a solution which is clearly a bad practice as the real app will crash with null values yet the bounty is allocated to answer that suggests a code change, can you please justly this? — Pavneet_Singh, Jul 20 '20 at 13:46
@Pavneet_Singh - Bounty is given to that answer because it has a link of why TextUtils.isEmpty(null) returns false (due to gradle default values param). It was my real project problem and that answer helped me in finding solution. It didn't have proper explanation so I wrote my answer too. — Harish Gyanani, Jul 22 '20 at 11:17
Have you tried running tests without `unitTests.returnDefaultValues` and with power mock implementation?, your mocked testutil,isempty should return false with powermock but `value.trim()` should throw an exception. if your test is passing, you have successfully implemented a useless test. — Pavneet_Singh, Jul 23 '20 at 13:11

score -1 · Answer 4 · answered Jul 11 '20 at 10:45

-1

Maybe instead of: value.trim().isEmpty()
try this: value.trim().equals("")

answered Jul 11 '20 at 10:45

LoukasPap

1,244
1
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java.lang.NullPointerException for null input in null safe static method

4 Answers4