     @_valueIdx = if _.isString @_valueCol then @_headers.indexOf(@_valueCol) else @_valueCol
 
     if @_keyIdx < 0 or @_valueIdx < 0
-      throw new Error("Something is wrong in lookup config: key '#{@_keyCol}' or value '#{@_valueCol}' column not found by name!.")
+      new Error("Something is wrong in lookup config: key '#{@_keyCol}' or value '#{@_valueCol}' column not found by name!.")
 
   _buildLookupMap: ->
     # create a property map with first occurrence of key (first to stay compatible with the previous _.find based implementation)

        @_values = @_headers = values = null
        this
    else
      @_setColumnIdx()
      @_buildLookupMap()
      Q(this)

        Q(@_lookupMap[safe])
      else
        fileMessage = if @_file then " File: #{@_file}." else ""
        new Error("Lookup transformation failed for value '#{safe}'.#{fileMessage} on lookup data:"
          + JSON.stringify(@_lookupMap, null, 4) + "most likely a missing lookup key")

class MultipartStringTransformer extends ValueTransformer
