@Test
public void testNullRequest() {

    final byte[] requestBody = "null".getBytes(StandardCharsets.UTF_8);
    final MockHttpServletRequest request = new MockHttpServletRequest();
    request.addHeader("X-Line-Signature", "SSSSIGNATURE");
    request.setContent(requestBody);
    doReturn(true).when(lineSignatureValidator).validateSignature(requestBody, "SSSSIGNATURE");
    assertThatThrownBy(() -> lineBotCallbackRequestParser.handle(request))
            .isInstanceOf(LineBotCallbackException.class)
            .hasMessage("Invalid content");
}