Getting a null pointer exception when invoking a method on a mock

I have a class:

open class Foo(private val bar: Bar) {
  fun print(): String {
    return bar.print()
  }
}

When I mock this class in java, I get a null pointer exception.

Foo foo = Mockito.mock(Foo.class);
when(foo.print()).thenReturn("value"); // Null pointer exception saying bar is null.

Foo foo = Mockito.mock(Foo.class);
doReturn("value").when(foo).print(); // Null pointer exception saying bar is null.

Foo foo = Mockito.mock(Foo.class);
doReturn("value").when(foo.print()); // Null pointer exception saying bar is null.

With mockito-kotlin:

foo = mock<Foo>()
whenever(foo.print()).thenReturn("value") // Null pointer exception saying bar is null.

How do you get around this?

[premnirmal]

Ok - figured it out - it is because the method is final.

the method needs to be marked open for this to work:

open class Foo(private val bar: Bar) {
    **open** fun print(): String {
        return bar.print()
    }
}

class Bar {
    fun print(): String {
        return "helle"
    }
}

@Test
fun test() {
    val foo = mock<Foo>()
    whenever(foo.print()).thenReturn("value")
    expect(foo.print()).toBe("value")
}

[argenkiwi]

In my case I was trying to mock a property which was annotated with @JvmField. Removing the annotation, which wasn’t needed in my case, did the trick.