@java.lang.Override
    public boolean containsLabels(java.lang.String key) {
      if (key == null) {
        throw new NullPointerException("map key");
      }
      return internalGetLabels().getMap().containsKey(key);
    }
<pre>
Optional. The labels applied to a resource must meet the following
requirements:

* Each resource can have multiple labels, up to a maximum of 64.
* Each label must be a key-value pair.
* Keys have a minimum length of 1 character and a maximum length of 63
  characters and cannot be empty. Values can be empty and have a maximum
  length of 63 characters.
* Keys and values can contain only lowercase letters, numeric characters,
  underscores, and dashes. All characters must use UTF-8 encoding, and
  international characters are allowed.
* The key portion of a label must be unique. However, you can use the same
  key with multiple resources.
* Keys must start with a lowercase letter or international character.

See [Google Cloud
Document](https://cloud.google.com/resource-manager/docs/creating-managing-labels#requirements)
for more details.
</pre>

<code>map&lt;string, string&gt; labels = 6 [(.google.api.field_behavior) = OPTIONAL];</code>
java-visionai/proto-google-cloud-visionai-v1/src/main/java/com/google/cloud/visionai/v1/IndexEndpoint.java