private void ensurePartsIsMutable() {
      if (!((bitField0_ & 0x00000002) != 0)) {
        parts_ = new java.util.ArrayList<com.google.cloud.vertexai.api.Part>(parts_);
        bitField0_ |= 0x00000002;
      }
    }
<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>

@param value The bytes for role to set.
@return This builder for chaining.
java-vertexai/proto-google-cloud-vertexai-v1/src/main/java/com/google/cloud/vertexai/api/Content.java