docs: public void removeDeferredTrailer(String hdr) {
          if (tc.isDebugEnabled()) {
              Tr.debug(tc, "removeDeferredTrailer(String): " + hdr);
          }
          if (null == hdr) {
              throw new IllegalArgumentException("Null header name");
          }
          this.knownTGs.remove(findKey(hdr));
      }