val schema = GraphQLUnionType.newUnionType().name("Shape")
                .possibleType(GraphQLTypeReference.typeRef("Circle"))
                .possibleType(GraphQLTypeReference.typeRef("Square"))
                .build()
val printer = SchemaPrinter()
printer.print(schema)

Exception in thread "main" java.lang.ClassCastException: class graphql.schema.GraphQLTypeReference cannot be cast to class graphql.schema.GraphQLUnmodifiedType (graphql.schema.GraphQLTypeReference and graphql.schema.GraphQLUnmodifiedType are in unnamed module of loader 'app')
	at graphql.schema.GraphQLTypeUtil.unwrapAll(GraphQLTypeUtil.java:199)
	at graphql.schema.DefaultGraphqlTypeComparatorRegistry.unwrapElement(DefaultGraphqlTypeComparatorRegistry.java:54)
	at graphql.schema.DefaultGraphqlTypeComparatorRegistry.lambda$sensibleGroupedOrder$0(DefaultGraphqlTypeComparatorRegistry.java:40)
	at java.base/java.util.TimSort.countRunAndMakeAscending(TimSort.java:355)
	at java.base/java.util.TimSort.sort(TimSort.java:220)
	at java.base/java.util.Arrays.sort(Arrays.java:1307)
	at java.base/java.util.stream.SortedOps$SizedRefSortingSink.end(SortedOps.java:353)
	at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:510)
	at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:499)
	at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:921)
	at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
	at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:682)
	at graphql.schema.idl.SchemaPrinter.lambda$unionPrinter$6(SchemaPrinter.java:626)
	at graphql.schema.idl.SchemaPrinter.printSchemaElement(SchemaPrinter.java:1079)
	at graphql.schema.idl.SchemaPrinter.print(SchemaPrinter.java:1052)
	at aero.airlab.common.ktable.support.TestSchemaKt.main(TestSchema.kt:36)
	at aero.airlab.common.ktable.support.TestSchemaKt.main(TestSchema.kt)