code: function getCellContent (field) {
    var entry = this
    var args = Array.prototype.slice.call(arguments, 1)
  
    if (typeof field === 'string') {
      return field
    }
    if (typeof field === 'function') {
      var value
      try {
        value = field.apply(entry, args)
      } catch (e) {
        value = '(err)'
      }
      if (value === undefined || value === null) {
        return ''
      }
  
      return value.toString()
    }
    return ''
  }
docs: Get the content of a cell. `field` is the function or string
  to use. `this` should be bound to the actual entry.
  Additional parameters are forwarded to the function `field`.
  @param  {Function|String} field
  @return {String}