public boolean isNullableSelf() {
        return nullableSelf;
    }
Returns if this JoinType can produce results that are {@code null} for
entities belonging to the same Stage where this JoinType is present.

@return if this JoinType can produce results that are {@code null} for
entities belonging to the same Stage where this JoinType is present
runtime-parent/runtime-join/src/main/java/com/speedment/runtime/join/stage/JoinType.java