title: MockMvc JsonPath result matcher doesn't match single value
body: <p>I am writing tests for my REST API controller and I need to check <code>UUID</code> value from returned <code>JSON</code> object, please see this test method:</p>
  
  <pre><code>@Test
  public void findById() throws Exception {
  
      final String uuidString = "6c2b1c8a-3c29-4160-98b0-b8eaea7ea4d1";
      final UUID id = UUID.fromString(uuidString);
      final Envelope envelope = createEnvelope(id);
  
      when(envelopeService.findOne(id, currentUser)).thenReturn(Optional.of(envelope));
      when(utilService.getLoggedInUser()).thenReturn(currentUser);
  
      mockMvc.perform(get("/api/envelopes/{id}", uuidString)).
              andExpect(status().isOk()).andExpect(content().contentType(Util.APPLICATION_JSON_UTF8))
              .andExpect(jsonPath("$..id", is(uuidString)));
  
      verify(envelopeService, times(1)).findOne(id, currentUser);
      //verifyNoMoreInteractions(envelopeService);
  
  }
  </code></pre>
  
  <p>but the test produces this error:</p>
  
  <pre><code> Expected: is "6c2b1c8a-3c29-4160-98b0-b8eaea7ea4d1"
           but: was &lt;["6c2b1c8a-3c29-4160-98b0-b8eaea7ea4d1"]&gt;
          at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:20)
          at org.springframework.test.util.JsonPathExpectationsHelper.assertValue(JsonPathExpectationsHelper.java:74)
          at org.springframework.test.web.servlet.result.JsonPathResultMatchers$1.match(JsonPathResultMatchers.java:86)
          at org.springframework.test.web.servlet.MockMvc$1.andExpect(MockMvc.java:171)
  </code></pre>
  
  <p>It seems that ID <code>6c2b1c8a-3c29-4160-98b0-b8eaea7ea4d1</code> is returned correctly but is in serialized into different structure. </p>
  
  <p><strong>What is wrong with my code?</strong></p>