Mapper implements Func1<From, To> { @Override public final To call(@Nonnull From from) { requireNotNull(from); return map(from); }  @Override final To call(@Nonnull From from); Collection<To> map(@Nonnull Collection<From> entities); abstract To map(From entity);  }
@Test public void callShouldNotRespectNulls() { checkIllegalArgumentException(() -> mapper.call(null)); }