NuCivic/nucivic-internal#232 Allowing dots and empty strings as valid

rvalues to be escaped.

NuCivic/nucivic-internal#232

### Acceptance test
- [ ] git pull
- [ ] run dkan_dataset.make
- [ ] Go to a resource
- [ ] Change a parameter whose value is a string with a dot or is an empty string
- [ ] Then a value in the url should be escaped