private com.google.protobuf.SingleFieldBuilderV3<
            com.google.cloud.tpu.v2alpha1.NetworkConfig,
            com.google.cloud.tpu.v2alpha1.NetworkConfig.Builder,
            com.google.cloud.tpu.v2alpha1.NetworkConfigOrBuilder>
        getNetworkConfigFieldBuilder() {
      if (networkConfigBuilder_ == null) {
        networkConfigBuilder_ =
            new com.google.protobuf.SingleFieldBuilderV3<
                com.google.cloud.tpu.v2alpha1.NetworkConfig,
                com.google.cloud.tpu.v2alpha1.NetworkConfig.Builder,
                com.google.cloud.tpu.v2alpha1.NetworkConfigOrBuilder>(
                getNetworkConfig(), getParentForChildren(), isClean());
        networkConfig_ = null;
      }
      return networkConfigBuilder_;
    }
<pre>
Network configurations for the TPU node. network_config and network_configs
are mutually exclusive, you can only specify one of them. If both are
specified, an error will be returned.
</pre>

<code>.google.cloud.tpu.v2alpha1.NetworkConfig network_config = 36;</code>
java-tpu/proto-google-cloud-tpu-v2alpha1/src/main/java/com/google/cloud/tpu/v2alpha1/Node.java