fix: 'Invalid Syntax : offending token '<EOF>'' when using Apollo persisted queries

[ObeyYourMaster]

(reopening of #653)
Hi, I've opened a pull request in https://github.com/graphql-java-kickstart/graphql-java-servlet as well, this fix depends on it. This pull request should fix the following issue:

When using Apollo persisted queries via angular-apollo I get the following error in browser console:
Invalid Syntax : offending token '<EOF>'

And the following in server console:
notprivacysafe.graphql.GraphQL : Query failed to parse : ''

Minimal reproduction: https://github.com/ObeyYourMaster/graphql-kickstart-spring-boot-apq-not-working-showcase

My angular setup:

package.json

{
  "@apollo/client": "3.3.20",
  "crypto-es": "1.2.7",
  "apollo-angular": "2.6.0"
}

ApolloClient setup:

export function createApollo(httpLink: HttpLink): ApolloClientOptions<any> {
  return {
    link: createPersistedQueryLink({
      sha256: (...args) => CryptoES.SHA256(...args).toString(),
    }).concat(httpLink.create({
      uri: environment.graphqlEndpoint,
    })),
    cache: new InMemoryCache(),
    defaultOptions: {
      query: {
        fetchPolicy: 'network-only'
      }
    }
  };
}

Used graphql-spring-boot versions:

        <dependency>
            <groupId>com.graphql-java-kickstart</groupId>
            <artifactId>graphql-kickstart-spring-boot-starter-webflux</artifactId>
            <version>11.1.0</version>
        </dependency>
        <dependency>
            <groupId>com.graphql-java-kickstart</groupId>
            <artifactId>graphql-kickstart-spring-boot-starter-tools</artifactId>
            <version>11.1.0</version>
        </dependency>

Please let me know your feedback/comments/thoughts in order to have the fix merged :)

[oliemansm]

Thanks @ObeyYourMaster !