Try to check null value with the Hamcrest assertThat assertion, but no idea how?

	@Test
	public void testApp()
        //ambiguous method call?
        assertThat(null, is(null));

1. Solution

1.1 To check null value, try is(nullValue), remember static import org.hamcrest.CoreMatchers.*

//hello static import, nullValue here
import static org.hamcrest.CoreMatchers.*;
import org.junit.Test;
//...
	@Test
	public void testApp()
        //true, check null
        assertThat(null, is(nullValue()));
        //true, check not null
        assertThat("a", is(notNullValue()));

1.2 Or this equivalent

import static org.hamcrest.CoreMatchers.*;
import org.hamcrest.core.IsNull;
import org.junit.Test;
//...
	@Test
	public void testApp()
        //true, check null
        assertThat(null, is(IsNull.nullValue()));
        //true, check not null
        assertThat("a", is(IsNull.notNullValue()));

The CoreMatchers.nullValue() above (1.1), is a shorthand for IsNull.nullValue, review the following source code :

public static org.hamcrest.Matcher<java.lang.Object> nullValue() {
    return org.hamcrest.core.IsNull.nullValue();

P.S Same to notNullValue()

References

1. Hamcrest – IsNull JavaDoc
2. Hamcrest official site