[Serializer] Handle circular references. symfony/symfony#12098.
feature #4299 [Serializer] Handle circular references. symfony/symfony#12098. (dunglas)

This PR was merged into the master branch.

Discussion
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[Serializer] Handle circular references. symfony/symfony#12098.

| Q             | A
| ------------- | ---
| Doc fix?      | no
| New docs?     | symfony/symfony#12098
| Applies to    | 2.6 or 2.7
| Fixed tickets | n/a

Commits
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1a1476e [Serializer] Handle circular references. symfony/symfony#12098.