     "source": [
      "class ReverseStringAlt(object):\n",
      "\n",
      "    def reverse_string_alt(string):\n",
      "        if string is None:\n",
      "            return None\n",
      "        return string[::-1]\n",
      "\n",
      "    def reverse_string_alt2(string):\n",
      "        if string is None:\n",
      "            return None\n",
 
</s> remove     "        if chars is None:\n",
    "            return None\n",
 </s> add     "        if chars is None or not chars:\n",
    "            return chars\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 string is None or not string:\n",
    "            return string\n",
     "source": [
      "class ReverseStringAlt(object):\n",
      "\n",
      "    def reverse_string_alt(string):\n",
    "        if string is None or not string:\n",
    "            return string\n",
    "        if string is None or not string:\n",
    "            return string\n",
      "        return string[::-1]\n",
      "\n",
      "    def reverse_string_alt2(string):\n",
      "        if string is None:\n",
      "            return None\n",
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