Validation fails when schema uses multi collection type for inquery parameters

[YuChem]

When validating document described by schema having this fragment

 "parameters": [
      {
          "name": "id",
          "in": "query",
          "description": "Filter the results by id. Multiple ids may be supplied.",
          "type": "array",
          "items": { "type": "integer" },
          "collectionFormat": "multi"
      },

validator throws an exception:

python3.5/site-packages/flex/validation/common.py", line 407, in generate_value_processor
    delimeter = DELIMETERS[collectionFormat]
KeyError: 'multi'

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