GraphQL schema is not generated when mutation input has Long generic type

[vtcosta]

I've been trying to run a similar solution as the one described in the issue 1928, but including mutations. Here is a similar example as the other issue, including a mutation, with a parameterized type of String:

public interface Attribute<T> {
    T getValue();
    void setValue(T value);
}

public class Greet implements Attribute<String> {
    private String value;

    public Greet() {}

    public Greet(String value) {
        this.value = value;
    }

    @Override
    public String getValue() {
        return this.value;
    }

    @Override
    public void setValue(String value) {
        this.value = value;
    }
}

    @Query
    public Greet sayHello(String value) {
        return new Greet(value);
    }

    @Mutation
    public boolean updateGreet(Greet greet) {
        return true;
    }

The example above seems to be working just fine. But if I change the parameterized type to Long, it will throw the exception graphql.AssertException: type Object not found in schema

Here is the example:

public class Greet implements Attribute<Long> {
    private Long value;

    public Greet() {}

    public Greet(Long value) {
        this.value = value;
    }

    @Override
    public Long getValue() {
        return this.value;
    }

    @Override
    public void setValue(Long value) {
        this.value = value;
    }
}

    @Query
    public Greet sayHello(Long value) {
        return new Greet(value);
    }

    @Mutation
    public boolean updateGreet(Greet greet) {
        return true;
    }

It seems this Long problem is specific for the mutation, because if I leave just the query, it works.