Confusing exception when regexp query used on numeric field

[clintongormley]

PUT t/t/1
{
  "num": 34
}

GET /_search
{
  "query": {
    "regexp": {
      "num": {
        "value": "34"
      }
    }
  }
}

returns:

"error": {
"root_cause": [
{
"type": "illegal_argument_exception",
"reason": "expected '"' at position 11"
}
],

[camilojd]

Hi, I created a fix for this in the referenced PR, that I believe does the right thing.

All tests pass.