private void ensurePartValIsMutable() {
        if (!partVal_.isModifiable()) {
          partVal_ = new com.google.protobuf.LazyStringArrayList(partVal_);
        }
        bitField0_ |= 0x00000004;
      }
<code>repeated string part_key = 2;</code>
@param value The bytes of the partKey to add.
@return This builder for chaining.
llap-common/src/gen/protobuf/gen-java/org/apache/hadoop/hive/llap/daemon/rpc/LlapDaemonProtocolProtos.java