@Override
  protected java.lang.Object standardSchemeReadValue(org.apache.thrift.protocol.TProtocol iprot, org.apache.thrift.protocol.TField field) throws org.apache.thrift.TException {
    _Fields setField = _Fields.findByThriftId(field.id);
    if (setField != null) {
      switch (setField) {
        case PUT:
          if (field.type == PUT_FIELD_DESC.type) {
            TPut put;
            put = new TPut();
            put.read(iprot);
            return put;
          } else {
            org.apache.thrift.protocol.TProtocolUtil.skip(iprot, field.type);
            return null;
          }
        case DELETE_SINGLE:
          if (field.type == DELETE_SINGLE_FIELD_DESC.type) {
            TDelete deleteSingle;
            deleteSingle = new TDelete();
            deleteSingle.read(iprot);
            return deleteSingle;
          } else {
            org.apache.thrift.protocol.TProtocolUtil.skip(iprot, field.type);
            return null;
          }
        default:
          throw new java.lang.IllegalStateException("setField wasn't null, but didn't match any of the case statements!");
      }
    } else {
      org.apache.thrift.protocol.TProtocolUtil.skip(iprot, field.type);
      return null;
    }
  }
Find the _Fields constant that matches name, or null if its not found.
hbase-thrift/src/main/java/org/apache/hadoop/hbase/thrift2/generated/TMutation.java