      "\n",
      "class ReverseString(object):\n",
      "\n",
      "    def reverse(self, chars):\n",
      "        if chars is None:\n",
      "            return None\n",
      "        size = len(chars)\n",
      "        for i in range(size//2):\n",
      "            chars[i], chars[size-1-i] = \\\n",
      "                chars[size-1-i], chars[i]\n",
      "        return chars"
 
</s> remove     "        if string is None:\n",
    "            return None\n",
 </s> add     "        if string is None or not string:\n",
    "            return string\n", </s> remove     "        if string is None:\n",
    "            return None\n",
 </s> add     "        if string is None or not string:\n",
    "            return string\n",
    "        if chars is None or not chars:\n",
    "            return chars\n",
      "\n",
      "class ReverseString(object):\n",
      "\n",
      "    def reverse(self, chars):\n",
    "        if chars is None or not chars:\n",
    "            return chars\n",
    "        if chars is None or not chars:\n",
    "            return chars\n",
      "        size = len(chars)\n",
      "        for i in range(size//2):\n",
      "            chars[i], chars[size-1-i] = \\\n",
      "                chars[size-1-i], chars[i]\n",
      "        return chars"
keep keep keep keep replace replace keep keep keep keep keep
 Update reverse string challenge (#113)

Update input check logic to check for an empty but not None entry. 
arrays_strings/reverse_string/reverse_string_solution.ipynb