at graphql.schema.GraphQLEnumType.getNameByValue(GraphQLEnumType.java:49)
    at graphql.schema.GraphQLEnumType.access$000(GraphQLEnumType.java:14)
    at graphql.schema.GraphQLEnumType$1.serialize(GraphQLEnumType.java:23)
    at graphql.execution.batched.BatchedExecutionStrategy.coerce(BatchedExecutionStrategy.java:219)
    at graphql.execution.batched.BatchedExecutionStrategy.handlePrimitives(BatchedExecutionStrategy.java:212)
    at graphql.execution.batched.BatchedExecutionStrategy.completeValues(BatchedExecutionStrategy.java:91)
    at graphql.execution.batched.BatchedExecutionStrategy.resolveField(BatchedExecutionStrategy.java:78)
    at graphql.execution.batched.BatchedExecutionStrategy.execute(BatchedExecutionStrategy.java:52)
    at graphql.execution.batched.BatchedExecutionStrategy.execute(BatchedExecutionStrategy.java:38)
    at graphql.execution.Execution.executeOperation(Execution.java:60)
    at graphql.execution.Execution.execute(Execution.java:33)
    at graphql.GraphQL.execute(GraphQL.java:78)
    at graphql.GraphQL.execute(GraphQL.java:55)
    at graphql.GraphQL.execute(GraphQL.java:47)
    at graphql.GraphQL.execute(GraphQL.java:43)
    at graphql.execution.batched.GraphqlExecutionSpec.runTestBatchingUnbatched(GraphqlExecutionSpec.groovy:40)
    at graphql.execution.batched.GraphqlExecutionSpec.runTest(GraphqlExecutionSpec.groovy:35)
    at graphql.execution.batched.GraphqlExecutionSpec.Legal null value for enum(GraphqlExecutionSpec.groovy:250)