Renamed empty_value to placeholder
feature #4486 Renamed empty_value to placeholder (WouterJ)

This PR was merged into the 2.6 branch.

Discussion
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Renamed empty_value to placeholder

| Q   | A
| --- | ---
| Doc fix? | no
| New docs? | yes (symfony/symfony#12003)
| Applies to | 2.6+
| Fixed tickets | #4261

Commits
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54c44ea Renamed empty_value to placeholder