public Builder mergeMetadata(com.google.protobuf.Struct value) {
      if (metadataBuilder_ == null) {
        if (((bitField0_ & 0x00000004) != 0)
            && metadata_ != null
            && metadata_ != com.google.protobuf.Struct.getDefaultInstance()) {
          getMetadataBuilder().mergeFrom(value);
        } else {
          metadata_ = value;
        }
      } else {
        metadataBuilder_.mergeFrom(value);
      }
      if (metadata_ != null) {
        bitField0_ |= 0x00000004;
        onChanged();
      }
      return this;
    }
<pre>
Input only. This field is for users to attach user managed metadata.
</pre>

<code>.google.protobuf.Struct metadata = 3 [(.google.api.field_behavior) = INPUT_ONLY];
</code>
java-visionai/proto-google-cloud-visionai-v1/src/main/java/com/google/cloud/visionai/v1/PacketHeader.java