En mi sitio web con react, me salen  los siguientes errores al compilar el react app:
Compiled with problems:
×
ERROR in ./src/components/Navbar.js
Module build failed (from ./node_modules/babel-loader/lib/index.js):
SyntaxError: D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\src\components\Navbar.js: JSX attributes must only be assigned a non-empty expression. (45:34)

  43 |                 <div id="userMenu" className={`${menuVisible ? 'show' : ''} ...`}>
  44 |                   <Link to="/perfil">Perfil</Link>
> 45 |                   <button onClick={/* función para cerrar sesión */}>Cerrar Sesión</button>
     |                                   ^
  46 |                 </div>
  47 |               </>
  48 |             ) : (
    at constructor (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:362:19)
    at FlowParserMixin.raise (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:3259:19)
    at FlowParserMixin.jsxParseAttributeValue (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:6653:16)
    at FlowParserMixin.jsxParseAttribute (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:6700:38)
    at FlowParserMixin.jsxParseOpeningElementAfterName (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:6714:28)
    at FlowParserMixin.jsxParseOpeningElementAt (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:6709:17)
    at FlowParserMixin.jsxParseElementAt (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:6733:33)
    at FlowParserMixin.jsxParseElementAt (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:6745:32)
    at FlowParserMixin.jsxParseElementAt (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:6745:32)
    at FlowParserMixin.jsxParseElement (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:6796:17)
    at FlowParserMixin.parseExprAtom (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:6806:19)
    at FlowParserMixin.parseExprSubscripts (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:10591:23)
    at FlowParserMixin.parseUpdate (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:10576:21)
    at FlowParserMixin.parseMaybeUnary (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:10556:23)
    at FlowParserMixin.parseMaybeUnaryOrPrivate (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:10410:61)
    at FlowParserMixin.parseExprOps (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:10415:23)
    at FlowParserMixin.parseMaybeConditional (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:10392:23)
    at FlowParserMixin.parseMaybeAssign (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:10355:21)
    at D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:5627:39
    at FlowParserMixin.tryParse (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:3597:20)
    at FlowParserMixin.parseMaybeAssign (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:5627:18)
    at D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:10325:39
    at FlowParserMixin.allowInAnd (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:11937:12)
    at FlowParserMixin.parseMaybeAssignAllowIn (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:10325:17)
    at FlowParserMixin.parseParenAndDistinguishExpression (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:11196:28)
    at FlowParserMixin.parseParenAndDistinguishExpression (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:5720:18)
    at FlowParserMixin.parseExprAtom (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:10849:23)
    at FlowParserMixin.parseExprAtom (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:6811:20)
    at FlowParserMixin.parseExprSubscripts (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:10591:23)
    at FlowParserMixin.parseUpdate (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:10576:21)
    at FlowParserMixin.parseMaybeUnary (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:10556:23)
    at FlowParserMixin.parseMaybeUnaryOrPrivate (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:10410:61)
    at FlowParserMixin.parseExprOps (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:10415:23)
    at FlowParserMixin.parseMaybeConditional (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:10392:23)
    at FlowParserMixin.parseMaybeAssign (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:10355:21)
    at FlowParserMixin.parseMaybeAssign (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:5678:18)
    at D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:10325:39
    at FlowParserMixin.allowInAnd (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:11937:12)
    at FlowParserMixin.parseMaybeAssignAllowIn (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:10325:17)
    at FlowParserMixin.tryParseConditionalConsequent (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:5152:29)
    at FlowParserMixin.parseConditional (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:5113:14)
    at FlowParserMixin.parseMaybeConditional (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:10396:17)
    at FlowParserMixin.parseMaybeAssign (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:10355:21)
    at FlowParserMixin.parseMaybeAssign (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:5678:18)
    at FlowParserMixin.parseExpressionBase (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:10309:23)
    at D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:10305:39
    at FlowParserMixin.allowInAnd (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:11937:12)
    at FlowParserMixin.parseExpression (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:10305:17)
    at FlowParserMixin.jsxParseExpressionContainer (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:6679:31)
    at FlowParserMixin.jsxParseElementAt (D:\Aplicaciones\XAMPP\htdocs\mi_sitio\frontend\react-app\node_modules\@babel\parser\lib\index.js:6758:36)
ERROR
[eslint] 
src\components\Navbar.js
  Line 45:34:  Parsing error: JSX attributes must only be assigned a non-empty expression. (45:34)