bug #20087 [2.8][VarDumper] Fix PHP 7.1 compat (nicolas-grekas)
bug #20087 [2.8][VarDumper] Fix PHP 7.1 compat (nicolas-grekas)

This PR was merged into the 2.8 branch.

Discussion
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[2.8][VarDumper] Fix PHP 7.1 compat

| Q             | A
| ------------- | ---
| Branch?       | 2.8
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | -
| License       | MIT
| Doc PR        | -

Fix PHP 7.1 nullable support.

Commits
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1e84452 [2.8][VarDumper] Fix PHP 7.1 compat

symfony/var-dumper,symfony/var-dumper