public Builder clearRole() {
      role_ = getDefaultInstance().getRole();
      bitField0_ = (bitField0_ & ~0x00000001);
      onChanged();
      return this;
    }
<pre>
Optional. The producer of the content. Must be either 'user' or 'model'.

Useful to set for multi-turn conversations, otherwise can be left blank
or unset.
</pre>

<code>string role = 1 [(.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/Content.java