public static void checkOut(DataOutput out) {
    if (out == null) {
      throw new NullPointerException("Null DataOutput");
    }
  }
Checks to make sure a {@code DataOutput} is not {@code null}.

@throws NullPointerException If {@code out} is {@code null}
geode-core/src/main/java/org/apache/geode/internal/InternalDataSerializer.java