Groovy mapping error for array: type must be compatible with java string

[tatianafrank]

I am integrating divolte with kafka. I have a custom event with a field that is an array of strings. I've defined the field in the avsc schema file like so:

{ "name": "countries", "type": ["null", {"type": "array", "items": "string"}]

and in the mapping.groovy file like so:
map eventParameter('countries') onto 'countries'
but I am getting the below error:

Exception in thread "main" io.divolte.server.recordmapping.SchemaMappingException: Cannot map the result of eventParameter(countries) onto field countries: type must be compatible with java.lang.String

Please tell me what I'm doing the wrong. This is a simple array such as:
"countries": ["us", "china"]

[tatianafrank]

I worked around this issue by using this format in the mapping.groovy file: map eventParameters().path('$.countries.*') onto 'countries'