     @walk_ @root_, toCodePoints(key), (node) ->
       prefix += fromCodePoint node.c
       callback prefix, node.v if node.v?
-    return @
+    return this
 
   keysWithinHammingDistance: (query, distance) ->
     items = []

    return null

  del: (key) ->
    return @ if !key?
    codepoints = toCodePoints key
    node = @find_ @root_, codepoints
    @delete_ node
    return @

  delete_: (node) ->
    return if !node?

      return if a.length != b.length
      callback key, node.v if calcHammingDistance(a, b) <= distance
      return
    return this

  searchWithinLevenshteinDistance: (query, distance, callback) ->
    a = toCodePoints query
