InvalidTypesException: Type of TypeVariable 'K' in 'class X' could not be determined

[Miguel Coimbra]

Hello,

I have some code which compiles correctly (Flink 1.4) under Java 8.
It uses generic types.
While it compiles correctly, the execution fails with the error:

org.apache.flink.api.common.functions.InvalidTypesException: Type of
TypeVariable 'K' in 'class X' could not be determined.

This is my main:

public static void main(final String[] args) {
    X<Long> x = new X();
}


This is my class X:

public class X<K> {

    public X() {
        TypeInformation<K> keySelector = TypeInformation.of(new
TypeHint<K>(){});
    }
}


Perhaps I'm lacking knowledge on the way Java's generics work, but why
can't Flink determine the TypeVariable of 'K'?
As I am instantiating X parameterized as a Long, that information should
eventually reach Flink and the constructor of X would be equivalent to this:

public X() {
    TypeInformation<Long> keySelector = TypeInformation.of(new
TypeHint<Long>(){});
}

During execution, however, this error pops up.
What am I missing here, and what is the best way to achieve this generic
behavior in a Flink-idiomatic way?

Thank you very much for your time.