code: public final void deleteAllContexts(SessionName parent) {
  
      DeleteAllContextsRequest request =
          DeleteAllContextsRequest.newBuilder()
              .setParent(parent == null ? null : parent.toString())
              .build();
      deleteAllContexts(request);
    }
docs: Deletes all active contexts in the specified session.
  
  <p>Sample code:
  
  <pre><code>
  try (ContextsClient contextsClient = ContextsClient.create()) {
  SessionName parent = SessionName.of("[PROJECT]", "[SESSION]");
  contextsClient.deleteAllContexts(parent);
  }
  </code></pre>
  
  @param parent Required. The name of the session to delete all contexts from. Format:
  `projects/&lt;Project ID&gt;/agent/sessions/&lt;Session ID&gt;` or `projects/&lt;Project
  ID&gt;/agent/environments/&lt;Environment ID&gt;/users/&lt;User ID&gt;/sessions/&lt;Session
  ID&gt;`. If `Environment ID` is not specified we assume default 'draft' environment. If
  `User ID` is not specified, we assume default '-' user.
  @throws com.google.api.gax.rpc.ApiException if the remote call fails