cannot build with gradle on fresh installed computer

[Bilal-S]

Receiving this error on running ./gradlew clean build command in plain vanilla java example
Env:

• Ubuntu 20.04
• opendJDK 11

import org.graphqlize.java.GraphQLResolver;
                          ^
  bad class file: /home/user/.gradle/caches/modules-2/files-2.1/org.graphqlize/graphqlize-java/0.1.0-alpha20/5abcf1eb56546b988aeff61fe2ea87d357a7cc36/graphqlize-java-0.1.0-alpha20.jar(/org/graphqlize/java/GraphQLResolver.class)
    class file has wrong version 59.0, should be 55.0
    Please remove or make sure it appears in the correct subdirectory of the classpath.
/home/user/code/graphqlize-demo/java/vanilla/src/main/java/Program.java:9: error: cannot access GraphQLizeResolver
import org.graphqlize.java.GraphQLizeResolver;
                          ^
  bad class file: /home/user/.gradle/caches/modules-2/files-2.1/org.graphqlize/graphqlize-java/0.1.0-alpha20/5abcf1eb56546b988aeff61fe2ea87d357a7cc36/graphqlize-java-0.1.0-alpha20.jar(/org/graphqlize/java/GraphQLizeResolver.class)
    class file has wrong version 59.0, should be 55.0
    Please remove or make sure it appears in the correct subdirectory of the classpath.
/home/user/code/graphqlize-demo/java/vanilla/src/main/java/Program.java:30: error: cannot find symbol
    GraphQLResolver graphQLResolver = new GraphQLizeResolver(dataSource);
    ^
  symbol:   class GraphQLResolver
  location: class Program
/home/user/code/graphqlize-demo/java/vanilla/src/main/java/Program.java:30: error: cannot find symbol
    GraphQLResolver graphQLResolver = new GraphQLizeResolver(dataSource);
                                          ^
  symbol:   class GraphQLizeResolver
  location: class Program
4 errors

[tamizhvendan]

Sorry @Bilal-S for the delayed reply.

It looks like a JDK specific issue.

Due to my current situation, I won't be able to fix this. If you send me an MR with the fix, I am open to review and merge.