Function UnsafeAppendNull

cpp/src/arrow/array/builder_base.h:225–225

  // Unsafe operations (don't check capacity/don't resize)

  void UnsafeAppendNull() { UnsafeAppendToBitmap(false); }

  // Append to null bitmap, update the length
  void UnsafeAppendToBitmap(bool is_valid) {