@java.lang.Override
  public Builder toBuilder() {
    return this == DEFAULT_INSTANCE ? new Builder() : new Builder().mergeFrom(this);
  }
<pre>
Required. Client side tenant identifier, used to uniquely identify the
tenant.

The maximum number of allowed characters is 255.
</pre>

<code>string external_id = 2 [(.google.api.field_behavior) = REQUIRED];</code>

@return The bytes for externalId.
java-talent/proto-google-cloud-talent-v4/src/main/java/com/google/cloud/talent/v4/Tenant.java