public class Foo {
  public byte[] getData(List<String> args) { ... }
}

public class MyTest {
  @Test
  public void myTest() {
    Foo mockFoo = mock(Foo.class);
    when(mockFoo.getData(any())).thenReturn(null);
  }
}

java.lang.IllegalStateException: This was not supposed to happen.
	at org.mockito.internal.util.reflection.GenericMetadataSupport$GenericArrayReturnType.rawType(GenericMetadataSupport.java:565)
	at org.mockito.internal.stubbing.answers.InvocationInfo.isVoid(InvocationInfo.java:98)
	at org.mockito.internal.stubbing.answers.Returns.validateFor(Returns.java:34)
	at org.mockito.internal.stubbing.InvocationContainerImpl.addAnswer(InvocationContainerImpl.java:65)
	at org.mockito.internal.stubbing.InvocationContainerImpl.addAnswer(InvocationContainerImpl.java:56)
	at org.mockito.internal.stubbing.OngoingStubbingImpl.thenAnswer(OngoingStubbingImpl.java:32)
	at org.mockito.internal.stubbing.BaseStubbing.thenReturn(BaseStubbing.java:34)
	at com.example.MyTest.myTest.(MyTest.java:50)
	... 38 trimmed
Caused by: java.lang.ClassNotFoundException: [Lbyte;
	at java.lang.Class.classForName(Native Method)
	at java.lang.Class.forName(Class.java:454)
	at org.mockito.internal.util.reflection.GenericMetadataSupport$GenericArrayReturnType.rawType(GenericMetadataSupport.java:556)
	... 46 more
Caused by: java.lang.ClassNotFoundException: byte
	at java.lang.Class.classForName(Native Method)
	at java.lang.BootClassLoader.findClass(ClassLoader.java:1358)
	at java.lang.BootClassLoader.loadClass(ClassLoader.java:1418)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:312)
	... 49 more
Caused by: java.lang.NoClassDefFoundError: Class not found using the boot class loader; no stack trace available