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

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