@java.lang.Override
    public void writeTo(com.google.protobuf.CodedOutputStream output) throws java.io.IOException {
      if (!com.google.protobuf.GeneratedMessageV3.isStringEmpty(metadataFilter_)) {
        com.google.protobuf.GeneratedMessageV3.writeString(output, 2, metadataFilter_);
      }
      if (vectorDbThresholdCase_ == 3) {
        output.writeDouble(3, (double) ((java.lang.Double) vectorDbThreshold_));
      }
      if (vectorDbThresholdCase_ == 4) {
        output.writeDouble(4, (double) ((java.lang.Double) vectorDbThreshold_));
      }
      getUnknownFields().writeTo(output);
    }
<pre>
Optional. String for metadata filtering.
</pre>

<code>string metadata_filter = 2 [(.google.api.field_behavior) = OPTIONAL];</code>

@return The bytes for metadataFilter.
java-vertexai/proto-google-cloud-vertexai-v1/src/main/java/com/google/cloud/vertexai/api/RagRetrievalConfig.java