code: public DoubleRange getMzRange() {
      if (isolationWindowMzLo != null && isolationWindowMzHi != null) {
        return new DoubleRange(isolationWindowMzLo, isolationWindowMzHi);
      }
      return null;
    }
docs: TODO: might be better to treat null values as infinity and always return non-null DoubleRange.
  Convenience method to get the precursor isolation window ange.
  
  @return null, if at least one range end is null (not set). Otherwise a new instance of {@link
  umich.ms.util.DoubleRange}