title: How to solve this exception Unexpected token < in JSON at position 0?
body: <p>I submitted the form using formik and added a mutation on button. Then, I got this exception below. How do I solve this exception?</p>
  <pre><code>Uncaught (in promise) Error: Network error: Unexpected token &lt; in JSON at position 0
      at new ApolloError (ApolloError.js:25)
      at Object.error (QueryManager.js:154)
      at notifySubscription (Observable.js:134)
      at onNotify (Observable.js:165)
      at SubscriptionObserver.error (Observable.js:224)
      at Object.error (bundle.esm.js:74)
      at notifySubscription (Observable.js:134)
      at onNotify (Observable.js:165)
      at SubscriptionObserver.error (Observable.js:224)
      at bundle.esm.js:135
  </code></pre>
  <p>Here I add my sample code of formik form with mutation. I am adding mutation is correct way? How to add mutation of a form?</p>
  <p>const { Form: AntForm, Row, Col, Button } = AntD;</p>
  <pre><code>    const POST_MUTATION = gql`
        mutation PostMutation($username: String!, $email: String!, 
       $password:String!){
          post(username: $username, email: $email, password: $password) {  
            username
            email
            password
          }
        }
      `
       class FormikApollo extends React.Component {
      
          state = {
              username: '',
              email: '',
              password: ''
          }
      
          render() {
              const { values, handleSubmit } = this.props
              const { username, email, password } = this.state
                 return (
                      &lt;Form onSubmit={handleSubmit}&gt;
                          &lt;Row gutter={4}&gt;
                              &lt;Col span={12} push={5}&gt;
                                  &lt;Field
                                      name=&quot;username&quot;
                                      label=&quot;Name&quot;
                                      placeholder=&quot;Enter a Name&quot;
                                      component={TextField}
                                      value={values.username}
                                      formitemlayout={formItemLayout}
      
                                  /&gt;
      
                                  &lt;Field
                                      name=&quot;email&quot;
                                      label=&quot;Email&quot;
                                      placeholder=&quot;Enter an Email&quot;
                                      component={TextField}
                                      value={values.email}
                                      formitemlayout={formItemLayout}
      
                                  /&gt;      
                                  &lt;Mutation mutation={POST_MUTATION} 
                          variables={{ username, email, password }}&gt;
                           {postMutation =&gt;
                                          &lt;Button type=&quot;primary&quot; htmlType=&quot;submit&quot; onClick={postMutation}&gt;Submit&lt;/Button&gt;
                                      }
                           
                      &lt;/Form&gt;
      
                  &lt;/div&gt;
      
              )
      
          }
      }
  </code></pre>
  <p>And my formik form is submitted by using handleSubmit with values</p>
  <pre><code>  const FormikApp = withFormik({
                      mapPropsToValues({ username, email, password }) {
                          return {
                              username: username || '',
                              email: email || '',
                              password: password || ''
                  
                          }
                      },
                     
                      handleSubmit(values, { resetForm, props }) {
                          resetForm();
                          console.log(values)
                      }
                  
                  })(FormikApollo)
                         
  </code></pre>