title: Flutter ferry custom scalar serializer "has non-dynamic type"
body: <p>I'm having a bit of a problem with a custom serializer in flutter ferry graphql package:</p>
  <p>I have used exactly the example from the ferry docs:
  <a href="https://ferrygraphql.com/docs/custom-scalars/#create-a-custom-serializer" rel="nofollow noreferrer">https://ferrygraphql.com/docs/custom-scalars/#create-a-custom-serializer</a></p>
  <p><strong>But I always get the following message when running the builder_runner:</strong></p>
  <pre><code>[SEVERE] built_value_generator:built_value on lib/schema.schema.gql.dart:
  Error in BuiltValueGenerator for abstract class GDailyForecastInput implements Built&lt;GDailyForecastInput, dynamic&gt;.
  Please make the following changes to use BuiltValue:
  
  1. Make field dateStart have non-dynamic type. If you are already specifying a type, please make sure the type is correctly imported.
  2. Make field dateEnd have non-dynamic type. If you are already specifying a type, please make sure the type is correctly imported.
  [SEVERE] built_value_generator:built_value on lib/schema.schema.gql.dart:
  Error in BuiltValueGenerator for abstract class GHourlyForecastInput implements Built&lt;GHourlyForecastInput, dynamic&gt;.
  Please make the following changes to use BuiltValue:
  
  1. Make field dateStart have non-dynamic type. If you are already specifying a type, please make sure the type is correctly imported.
  2. Make field dateEnd have non-dynamic type. If you are already specifying a type, please make sure the type is correctly imported.
  </code></pre>
  <p>dateStart and dateEnd are query input values of type Date
  This is my type overwrite:
  type_overrides:
  Date:
  name: Date
  Does anyone one why this error happens?
  I really can't find out what the problem is</p>
  <p><strong>Date is define das a scalar in my schema.graphql file:</strong></p>
  <pre><code>&quot;&quot;&quot;A date string with format `Y-m-d`, e.g. `2011-05-23`.&quot;&quot;&quot;
  scalar Date
  </code></pre>
  <p><strong>Here is my build.yaml file:</strong></p>
  <pre><code>targets:
    $default:
      builders:
        gql_build|schema_builder:
          enabled: true
          options:
            type_overrides:
              Date:
                name: Date
                
        gql_build|ast_builder:
          enabled: true
          options:
            type_overrides:
              Date:
                name: Date
  
        gql_build|data_builder:
          enabled: true
          options:
            type_overrides:
              Date:
                name: Date
            schema: appdemo|lib/schema.graphql
  
        gql_build|var_builder:
          enabled: true
          options:
            type_overrides:
              Date:
                name: Date
            schema: appdemo|lib/schema.graphql
  
        gql_build|serializer_builder:
          enabled: true
          options:
            schema: appdemo|lib/schema.graphql
            custom_serializers:
              - import: './serializers/date_serializer.dart'
                name: DateSerializer
  
        ferry_generator|req_builder:
          enabled: true
          options:
            type_overrides:
              Date:
                name: Date
            schema: appdemo|lib/schema.graphql
  </code></pre>
  <p>I tried debugging already. If I rename my scalar to <code>DateTime</code> everything works fine.
  (I also have a scalar <code>DateTime</code> in my <code>schema.graphql</code> file.)
  It's only if I use the name <code>Date</code> that I get this error.</p>
  <p><strong>Am I missing something?</strong>
  Do I need to create additionally to the code in the documention a dart <code>Date</code> class and link it or so?</p>