def create_custom_field!(params)      
      response = @@soap.createListCustomField(
      :apiKey => @apiKey,
      :listID => @listID,
      :fieldName => params[:fieldName],
      :dataType => params[:dataType],
      :options => params.fetch(:options, "") 
      )
      handle_response response.list_CreateCustomFieldResult
    end
def create_custom_field!(params)      
      response = @@soap.createListCustomField(
      :apiKey => @apiKey,
      :listID => @listID,
      :fieldName => params[:fieldName],
      :dataType => params[:dataType],
      :options => params.fetch(:options, "") 
      )
      handle_response response.list_CreateCustomFieldResult
    end
Creates a new custom field for a list

Available _params_ argument are:
   * :fieldName - The Name for the new Custom Field. This will be used to generate the custom fields Key.
   * :dataType - The Data Type for the new Custom Field. This must be one of Text, Number, MultiSelectOne, or MultiSelectMany
   * :options - The available options for a multi-valued custom field. Options should be an Array of Strings, like: %w[Brazil Ireland England].
                You can't pass this field for Text and Number custom fields

*Return*:

*Success*: Upon a successful call, this method will return a Campaigning::Result object wich consists of a +code+ and +message+ fields
containing a successful message.

*Error*: An Exception containing the cause of the error will be raised.