Getting incompatible return type error when extending FungibleToken in Java

[LHao87]

There is a question asked long time ago:
https://stackoverflow.com/questions/57650475/error-when-extending-fungibletoken-supportedschemas-in-queryablestate-clashes

As shown in the question, when extending FungibleToken, it will get the error of incompatible return type. This only happens when writing in Java. Kotlin works just fine.
This could be because the supportedSchemas() in the FungibleToken does not specify its return type.

That's to say, if we change the supportedSchemas() method in the FungibleToken from
override fun supportedSchemas() = listOf(FungibleTokenSchemaV1)
to
override fun supportedSchemas() : Iterable<MappedSchema> = listOf(FungibleTokenSchemaV1)
Then the error will disappear.