public Builder mergeCustomVoice(com.google.cloud.texttospeech.v1beta1.CustomVoiceParams value) {
      if (customVoiceBuilder_ == null) {
        if (((bitField0_ & 0x00000008) != 0)
            && customVoice_ != null
            && customVoice_
                != com.google.cloud.texttospeech.v1beta1.CustomVoiceParams.getDefaultInstance()) {
          getCustomVoiceBuilder().mergeFrom(value);
        } else {
          customVoice_ = value;
        }
      } else {
        customVoiceBuilder_.mergeFrom(value);
      }
      if (customVoice_ != null) {
        bitField0_ |= 0x00000008;
        onChanged();
      }
      return this;
    }
<pre>
The configuration for a custom voice. If [CustomVoiceParams.model] is set,
the service will choose the custom voice matching the specified
configuration.
</pre>

<code>.google.cloud.texttospeech.v1beta1.CustomVoiceParams custom_voice = 4;</code>
java-texttospeech/proto-google-cloud-texttospeech-v1beta1/src/main/java/com/google/cloud/texttospeech/v1beta1/VoiceSelectionParams.java