old_contents: /**
   * Join filter
   */
  
  export const name = 'join'
  export const alias = '&'
  
  /**
   * Joins an array of strings.
   *
   * @param {Array} inputStrings
   * @param {String} param
   * @returns {String}
   */
  export function apply (inputStrings, param) {
  
    // make sure that input strings is an array
    if (!(inputStrings instanceof Array)) return inputStrings
  
    // get delimiter
    let delimiter = param
  
    // filter out empty strings
    inputStrings = inputStrings.filter((inputString) => {
      return inputString && inputString.length
    })
  
    // join strings using delimiter
    return inputStrings.join(delimiter)
  }
  
new_contents: /**
   * Join filter
   */
  
  export const name = 'join'
  export const alias = '&'
  
  /**
   * Joins an array of strings.
   *
   * @param {Array} inputStrings
   * @param {String} param
   * @returns {String}
   */
  export function apply (inputStrings, param) {
  
    // make sure that input strings is an array
    if (!(inputStrings instanceof Array)) return inputStrings
  
    // TODO fix this upstream, in populator
    inputStrings = inputStrings.map(str => {
      if (str instanceof Object && str.hasOwnProperty('hasValueForKey')) {
        return str.populated
      }
      else {
        return str
      }
    })
  
    // get delimiter
    let delimiter = param
  
    // filter out empty strings
    inputStrings = inputStrings.filter((inputString) => {
      return inputString && inputString.length
    })
  
    // join strings using delimiter
    return inputStrings.join(delimiter)
  }
  
subject: Fix for join filter in XD