docs: synchronized final JsMsgPart getHdr2() {
          if (hdr2 == null) {
              if (TraceComponent.isAnyTracingEnabled() && tc.isDebugEnabled())
                  SibTr.debug(this, tc, "getHdr2 will call getPart");
              hdr2 = jmo.getPart(JsHdrAccess.HDR2, JsHdr2Access.schema);
          }
          return hdr2;
      }