public Builder addChannels(
          int index, com.google.cloud.vertexai.api.SlackSource.SlackChannels.SlackChannel value) {
        if (channelsBuilder_ == null) {
          if (value == null) {
            throw new NullPointerException();
          }
          ensureChannelsIsMutable();
          channels_.add(index, value);
          onChanged();
        } else {
          channelsBuilder_.addMessage(index, value);
        }
        return this;
      }
<pre>
Required. The Slack channel IDs.
</pre>

<code>
repeated .google.cloud.vertexai.v1.SlackSource.SlackChannels.SlackChannel channels = 1 [(.google.api.field_behavior) = REQUIRED];
</code>
java-vertexai/proto-google-cloud-vertexai-v1/src/main/java/com/google/cloud/vertexai/api/SlackSource.java