class Avo::BaseController

def cast_nullable(params)
  fields = @resource.get_field_definitions
  nullable_fields = fields.filter do |field|
    field.nullable
  end
    .map do |field|
    [field.id, field.null_values]
  end
    .to_h
  params.each do |key, value|
    nullable = nullable_fields[key.to_sym]
    if nullable.present? && value.in?(nullable)
      params[key] = nil
    end
  end
  params
end