Handle nil and empty string content edge-cases

[abrom]

Resolves #94

Handle nil input case by treating it as an empty string (convert all input to a string with to_s)

Handle empty string case in the processor by passing a single space to Puppeteer instead. Likely cause is that Puppeteer is taking an empty string to mean "not provided" and thus ignoring the call to respond, instead choosing to wait for further input.. which never comes:

https://github.com/puppeteer/puppeteer/blob/v5.5.0/docs/api.md#httprequestrespondresponse

[abrom]

@alexwbuschle how does this look to you? It also means that Grover would "deal" with other input types too.. ie if someone passed in some other type than a String (or NilClass)

[alexwbuschle]

👏