@Override
  public Object selectValue(String queryPredicate) throws FunctionDomainException,
      TypeMismatchException, NameResolutionException, QueryInvocationTargetException {
    SelectResults result = query(queryPredicate);
    if (result.isEmpty()) {
      return null;
    }
    if (result.size() > 1) {
      throw new FunctionDomainException(
          String.format("selectValue expects results of size 1, but found results of size %s",
              result.size()));
    }
    return result.iterator().next();
  }
This instance method was added so that unit tests could mock it
geode-core/src/main/java/org/apache/geode/internal/cache/LocalDataSet.java