private com.google.protobuf.SingleFieldBuilderV3<
            com.google.cloud.tpu.v2.ServiceAccount,
            com.google.cloud.tpu.v2.ServiceAccount.Builder,
            com.google.cloud.tpu.v2.ServiceAccountOrBuilder>
        getServiceAccountFieldBuilder() {
      if (serviceAccountBuilder_ == null) {
        serviceAccountBuilder_ =
            new com.google.protobuf.SingleFieldBuilderV3<
                com.google.cloud.tpu.v2.ServiceAccount,
                com.google.cloud.tpu.v2.ServiceAccount.Builder,
                com.google.cloud.tpu.v2.ServiceAccountOrBuilder>(
                getServiceAccount(), getParentForChildren(), isClean());
        serviceAccount_ = null;
      }
      return serviceAccountBuilder_;
    }
<pre>
The Google Cloud Platform Service Account to be used by the TPU node VMs.
If None is specified, the default compute service account will be used.
</pre>

<code>.google.cloud.tpu.v2.ServiceAccount service_account = 37;</code>
java-tpu/proto-google-cloud-tpu-v2/src/main/java/com/google/cloud/tpu/v2/Node.java