<p>I was working on the Grommet getting started example and encountered this error when adding the <code><AppBar></code> tag: </p> <pre class="brush:php;toolbar:false;">defaultValidatorFn is not a function TypeError: defaultValidatorFn is not a function at shouldForwardProp (http://localhost:3000/main.c6cdacb143c3e873b1fb.hot-update.js:4491:12) at http://localhost:3000/main.c6cdacb143c3e873b1fb.hot-update.js:11014:142 at D (http://localhost:3000/main.c6cdacb143c3e873b1fb.hot-update.js:11023:6) at renderWithHooks (http://localhost:3000/static/js/bundle.js:31049:22) at updateForwardRef (http://localhost:3000/static/js/bundle.js:33620:24) at beginWork (http://localhost:3000/static/js/bundle.js:35667:20) at HTMLUnknownElement.callCallback (http://localhost:3000/static/js/bundle.js:20641:18) at Object.invokeGuardedCallbackDev (http://localhost:3000/static/js/bundle.js:20685:20) at invokeGuardedCallback (http://localhost:3000/static/js/bundle.js:20742:35) at beginWork$1 (http://localhost:3000/static/js/bundle.js:40616:11)</pre> <p>Upon further inspection, the console displays a series of warnings, as shown below: </p> <pre class="brush:php;toolbar:false;">styled-components: it looks like an unknown prop "full" is being sent through to the DOM, which will likely trigger a React console error</pre> ; <p>I tried<code>yarn add @emotion/is-prop-valid</code>but it made no difference. What am I doing wrong here? </p>