private com.google.protobuf.SingleFieldBuilderV3<
            com.google.cloud.vmwareengine.v1.HcxActivationKey,
            com.google.cloud.vmwareengine.v1.HcxActivationKey.Builder,
            com.google.cloud.vmwareengine.v1.HcxActivationKeyOrBuilder>
        getHcxActivationKeyFieldBuilder() {
      if (hcxActivationKeyBuilder_ == null) {
        hcxActivationKeyBuilder_ =
            new com.google.protobuf.SingleFieldBuilderV3<
                com.google.cloud.vmwareengine.v1.HcxActivationKey,
                com.google.cloud.vmwareengine.v1.HcxActivationKey.Builder,
                com.google.cloud.vmwareengine.v1.HcxActivationKeyOrBuilder>(
                getHcxActivationKey(), getParentForChildren(), isClean());
        hcxActivationKey_ = null;
      }
      return hcxActivationKeyBuilder_;
    }
<pre>
Required. The initial description of a new HCX activation key. When
creating a new key, this field must be an empty object.
</pre>

<code>
.google.cloud.vmwareengine.v1.HcxActivationKey hcx_activation_key = 2 [(.google.api.field_behavior) = REQUIRED];
</code>
java-vmwareengine/proto-google-cloud-vmwareengine-v1/src/main/java/com/google/cloud/vmwareengine/v1/CreateHcxActivationKeyRequest.java