bug #17527 fixed undefined variable (fabpot)

This PR was merged into the 2.3 branch.

Discussion
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fixed undefined variable

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #16653
| License       | MIT
| Doc PR        | n/a

Commits
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4b21351 fixed undefined variable

src/Symfony/Bundle/WebProfilerBundle/Resources/views/Profiler/toolbar_item.html.twig

@@ -1,4 +1,4 @@
-{% if link %}
+{% if link|default(true) %}
     {% set icon %}
         <a href="{{ path('_profiler', { 'token': token, 'panel': name }) }}">{{ icon }}</a>
     {% endset %}