public com.google.protobuf.ByteString getServiceAccountBytes() {
        java.lang.Object ref = serviceAccount_;
        if (ref instanceof String) {
          com.google.protobuf.ByteString b =
              com.google.protobuf.ByteString.copyFromUtf8((java.lang.String) ref);
          serviceAccount_ = b;
          return b;
        } else {
          return (com.google.protobuf.ByteString) ref;
        }
      }
<pre>
Optional. The user-managed service account to which to delegate service
agent permissions. You can grant Cloud Storage bucket permissions to this
service account instead of to the Transfer Service service agent.

Format is
`projects/-/serviceAccounts/ACCOUNT_EMAIL_OR_UNIQUEID`

Either the service account email
(`SERVICE_ACCOUNT_NAME&#64;PROJECT_ID.iam.gserviceaccount.com`) or the unique
ID (`123456789012345678901`) are accepted in the string. The `-`
wildcard character is required; replacing it with a project ID is invalid.

See
https://cloud.google.com//storage-transfer/docs/delegate-service-agent-permissions
for required permissions.
</pre>

<code>string service_account = 18 [(.google.api.field_behavior) = OPTIONAL];</code>

@return The bytes for serviceAccount.
java-storage-transfer/proto-google-cloud-storage-transfer-v1/src/main/java/com/google/storagetransfer/v1/proto/TransferTypes.java