Ambiguity.java

import java.util.Collection;

public class Ambiguity {
	public void foo(CriteriaBuilder builder) {
    // change Object -> Number (or any other type) and it compiles
		Expression<Object> objectExpression = null;
		Expression<Collection<Object>> collectionOfObjectExpression = null;
		builder.isNotMember(objectExpression, collectionOfObjectExpression);
	}
}

class Expression<T> { }

class CriteriaBuilder {
  public <E,C extends Collection<E>> void isNotMember(E elem, Expression<C> collection) {}
  public <E,C extends Collection<E>> void isNotMember(Expression<E> elem, Expression<C> collection) {}
}

@otrosien has a workaround in the other gist I created: https://gist.github.com/olivergierke/c644327bb89191f2b52e298427ebf201