title: java.lang.IllegalArgumentException: Unrecognized Type: [null]
body: <p>I have the following structure in the Spring MVC project I have created. </p>
  
  <pre><code>public class CustomerTest {
  //@Mock
  //private Customer customer;
   @Mock
   private CustomerService service; 
  
   @InjectMocks 
   private CustomersController custcontroller; 
   private MockMvc mockmvc;
  /* Before executes before each and every test */
  @Before
  public void setup() {
      MockitoAnnotations.initMocks(this);
      mockmvc = MockMvcBuilders.standaloneSetup(custcontroller).build();
  
  }
  
  /*test that our requests are being sent*/
  
  @Test
  public void getExistingCustomerEntry() throws Exception {
      // assertEquals(expected parameter,your parameter)
      Customer cust = new Customer();
      cust.setCustomer_id(1L);
      cust.setName("sam");
      when(service.find(1L)).thenReturn(cust);
      try {
      mockmvc.perform(get("/rest/cust-entries/1"))
      .andExpect((jsonPath("$.name", Is.is(cust.getName()))))
      .andExpect(jsonPath("$.links[*].href", hasItem(endsWith("/cust-entries/1"))))
      .andExpect(status().isOk())
      .andDo(print());
      } catch(Exception e) {
          throw e;
      }
  }
  }
  </code></pre>
  
  <p>The Controller Class is as below :</p>
  
  <pre><code>@Controller
  public class CustomersController {
      private CustomerService service; 
  
  public CustomersController(CustomerService service) {
      this.service = service;
  }
  /*used a path variable to allow to bind a variable in the url to the Java variable*/
  @RequestMapping(value = "/rest/cust-entries/{customer_id}", method= RequestMethod.GET)
  public ResponseEntity&lt;CustomerResource&gt; getCustomerEntry(@PathVariable Long customer_id) {
    Customer custEntry = service.find(customer_id);
    System.out.println("Was here" + customer_id);
    CustomerResource resource = new CustomerServiceEntryAsm().toResource(custEntry);
    return new ResponseEntity&lt;CustomerResource&gt;(resource,HttpStatus.OK);
  }
  
  }
  </code></pre>
  
  <p>I get the following error message after running the CustomerTest class</p>
  
  <pre><code>CustomerTest
  </code></pre>
  
  <p>test.java.CustomerTest
  getExistingCustomerEntry(test.java.CustomerTest)
  org.springframework.web.util.NestedServletException: Request processing failed; nested exception is java.lang.IllegalArgumentException: Unrecognized Type: [null]</p>
  
  <pre><code>at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:981)
  
  at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:860)
  
  at javax.servlet.http.HttpServlet.service(HttpServlet.java:620)
  
  at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:845)
  
  at org.springframework.test.web.servlet.TestDispatcherServlet.service(TestDispatcherServlet.java:65)
  
  at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
  
  at org.springframework.mock.web.MockFilterChain$ServletFilterProxy.doFilter(MockFilterChain.java:167)
  
  at org.springframework.mock.web.MockFilterChain.doFilter(MockFilterChain.java:134)
  
  at org.springframework.test.web.servlet.MockMvc.perform(MockMvc.java:155)
  
  at test.java.CustomerTest.getExistingCustomerEntry(CustomerTest.java:74)
  
  at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  
  at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
  
  at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
  
  at java.lang.reflect.Method.invoke(Method.java:497)
  
  at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
  
  at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
  
  at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
  
  at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
  
  at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
  
  at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:325)
  
  at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:78)
  
  at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:57)
  
  at org.junit.runners.ParentRunner$3.run(ParentRunner.java:290)
  
  at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:71)
  
  at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:288)
  
  at org.junit.runners.ParentRunner.access$000(ParentRunner.java:58)
  
  at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:268)
  
  at org.junit.runners.ParentRunner.run(ParentRunner.java:363)
  
  at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
  
  at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
  
  at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:459)
  
  at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:675)
  
  at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:382)
  
  at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:192)
  </code></pre>
  
  <p>Caused by: java.lang.IllegalArgumentException: Unrecognized Type: [null]</p>
  
  <pre><code>at com.fasterxml.jackson.databind.type.TypeFactory._fromAny(TypeFactory.java:1109)
  
  at com.fasterxml.jackson.databind.type.TypeFactory.constructType(TypeFactory.java:566)
  
  at com.fasterxml.jackson.databind.type.TypeFactory.constructType(TypeFactory.java:602)
  
  at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.getJavaType(AbstractJackson2HttpMessageConverter.java:311)
  
  at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.writeInternal(AbstractJackson2HttpMessageConverter.java:249)
  
  at org.springframework.http.converter.AbstractGenericHttpMessageConverter.write(AbstractGenericHttpMessageConverter.java:100)
  
  at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:222)
  
  at org.springframework.web.servlet.mvc.method.annotation.HttpEntityMethodProcessor.handleReturnValue(HttpEntityMethodProcessor.java:183)
  
  at org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue(HandlerMethodReturnValueHandlerComposite.java:80)
  
  at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:126)
  
  at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:814)
  
  at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:737)
  
  at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:85)
  
  at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:959)
  
  at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:893)
  
  at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:969)
  
  ... 33 more
  </code></pre>
  
  <p>I debugged the junit test and the controller class and there is a null argument exception on the return type of the resource on the following line</p>
  
  <pre><code>return new ResponseEntity&lt;CustomerResource&gt;(resource,HttpStatus.OK);
  </code></pre>
  
  <p>What am I doing wrong here?</p>