@Override
  protected InputStream readInputStreamParam(String key) {
    Part part = readPart(key);
    return (part == null) ? null : part.getInputStream();
  }
@Test
  public void return_no_input_stream_when_content_type_is_null() {
    when(source.getContentType()).thenReturn(null);

    assertThat(underTest.readInputStreamParam("param1")).isNull();
  }