public Builder clearMetadataFilter() {
        metadataFilter_ = getDefaultInstance().getMetadataFilter();
        bitField0_ = (bitField0_ & ~0x00000004);
        onChanged();
        return this;
      }
<pre>
Optional. String for metadata filtering.
</pre>

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

@return This builder for chaining.
java-vertexai/proto-google-cloud-vertexai-v1/src/main/java/com/google/cloud/vertexai/api/RagRetrievalConfig.java