Error ArrayStructureDumper

[ComteZeroVD]

| Bundle version "^1.6" |
| Symfony version 4 |
| PHP version 7.2 |

I have this field in a form

$builder->add('moisdepart', ChoiceType::class, [
              'choices' => [
                '01' => '01',
                '02' => '02',
                '03' => '03',
                '04' => '04',
                '05' => '05',
                '06' => '06',
                '07' => '07',
                '08' => '08',
                '09' => '09',
                '10' => '10',
                '11' => '11',
                '12' => '12',
              ],
              'label' => 'Mois de départ',
              'required' => false,
            ]);

When I use the command
translation:extract fr --config=app --keep --output-format=yml

I get this message

In ArrayStructureDumper.php line 53:
                                                             
  explode() expects parameter 2 to be string, integer given  

A dump on $id shows that I get the error once it gets to the choice "10" and after, because it is considered as an integer.