Error if an enum field allows null and is invalid

[rflorence]

Ajv requires that nullable enum fields include null in the enum array with a schema like this:

{
  type: 'object',
  properties: {
    test: {
      type: 'string',
      enum: ['a', 'b', null],
      nullable: true
    },
    metadata: reviewMetadataSchema
  },
}

If you pass in { test: 'c' } then ajv.errors will look like this

[
  {
    instancePath: '/test',
    schemaPath: '#/properties/test/enum',
    keyword: 'enum',
    params: {
        allowedValues: ['a', 'b', null]
    },
    message: 'must be equal to one of the allowed values'
  }
]

and better-ajv-errors will throw an error like this

TypeError: Cannot read properties of null (reading 'length')
    at leven (/node_modules/leven/index.js:14:11)
    at /node_modules/better-ajv-errors/src/validation-errors/enum.js:63:17
    at Array.map (<anonymous>)
    at EnumValidationError.findBestMatch (/node_modules/better-ajv-errors/src/validation-errors/enum.js:61:8)
    at EnumValidationError.getError (/node_modules/better-ajv-errors/src/validation-errors/enum.js:30:28)
    at customErrorToStructure (/node_modules/better-ajv-errors/src/index.js:11:49)
    at Array.map (<anonymous>)
    at src_default (/node_modules/better-ajv-errors/src/index.js:22:25)

Without the null in the enum, better-ajv-errors will work as expected, but then you can't make the property nullable.