             wordLength: wordLength, prefix: [DawgLetter](), filled: filled,
             filledCount: filled.count, source: rootNode,
             blankLetter: String(blankLetter).utf8.first!, results: &results)
-        return results
+        return results.count > 0 ? results : nil
     }
 }
        withLetters letters: [Character],
        wordLength: Int,
        filledLetters: [Int: Character] = [Int: Character](),
        blankLetter: Character = "?") -> [String]
    {
        var filled = [Int: DawgLetter]()
        for (key, value) in filledLetters {

                while char != newLine
                {
                    buffer.append(char)
                    i += 1
                    if i >= characters.count { break }
                    char = characters[i]
                }
                dawg.insert(buffer)
                buffer.removeAll()
                i += 1
            } while i != characters.count
            dawg.minimize(0)
            dawg.save(outputPath)
