docs: public boolean isValueTypeUniqueIndexable(StringBuffer msg) {
          // This call to isValueTypeIndexable is needed because
          // all comparison, all conjunction, and some operator expressions
          // need to refine it to compensate for their false claims that
          // their value types (actually non-indexable boolean) is BIGINT.
          // that their value type is actually boolean.
          // If they were fixed, isValueTypeIndexable and
          // isValueTypeUniqueIndexable could be replaced by VoltType functions.
          if (!isValueTypeIndexable(msg)) {
              return false;
          }
          if (!m_valueType.isUniqueIndexable()) {
              msg.append("expression of type " + m_valueType.getName());
              return false;
          }
          return true;
      }