private void ensureAllowedFunctionNamesIsMutable() {
      if (!allowedFunctionNames_.isModifiable()) {
        allowedFunctionNames_ = new com.google.protobuf.LazyStringArrayList(allowedFunctionNames_);
      }
      bitField0_ |= 0x00000002;
    }
<pre>
Optional. Function calling mode.
</pre>

<code>
.google.cloud.vertexai.v1.FunctionCallingConfig.Mode mode = 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/FunctionCallingConfig.java