title: Spring Boot 2 / GraphQL Extended Scalars not working: Exception "Cannot construct instance" "cannot deserialize"
body: <p>I've got a working setup for a GraphQL API (Spring Boot 2, GraphQL Spring Boot Starter, GraphiQL). </p>
  
  <p>Then I tried to introduce a custom scalar provided by the library <em>graphql-java-extended-scalars</em> (in this case the <em>DateScalar</em> for a member with the type <em>java.time.LocalDate</em>):</p>
  
  <p>I declared the custom scalar and the type in the schema,</p>
  
  <pre><code>scalar Date
  ...
    somedate: Date
  ...
  </code></pre>
  
  <p>I provided <code>GraphQLScalarType</code> as a Spring Bean (otherwise the server wouldn't start up):</p>
  
  <pre class="lang-java prettyprint-override"><code>@Bean
  public GraphQLScalarType date() {
     return ExtendedScalars.Date;
  }
  </code></pre>
  
  <p>I executed a mutation query with a <em>Date</em>. </p>
  
  <pre class="lang-js prettyprint-override"><code>mutation {
    createSomething(
      something:{
        ...
        somedate: "2018-07-20",
        ...
      }
    )
  }
  </code></pre>
  
  <p>But unfortunately I get this exception,</p>
  
  <pre><code>com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of `java.time.LocalDate` (no Creators, like default construct, exist): cannot deserialize from Object value (no delegate- or property-based Creator)
  </code></pre>
  
  <p>After some hours of research, I have no idea what could be wrong. It seems that the Scalar was not picked up despite provided in the configuration. </p>
  
  <p>The <code>GraphQLInputType</code> looks like this,</p>
  
  <pre class="lang-java prettyprint-override"><code>@Data
  public class Something implements GraphQLInputType {
  
      ...
      private LocalDate somedate;
      ...
  
      @Override
      public String getName() {
          return "Something";
      }
  }
  </code></pre>