Get request to api_capabilities using query values that don't exist return null

[ericholguin]

I'm submitting a ...

• bug report
• new feature / enhancement request
• improvement request (usability, performance, tech debt, etc.)
• other

Traffic Control components affected ...

• CDN in a Box
• Documentation
• Grove
• Traffic Control Client
• Traffic Monitor
• Traffic Ops
• Traffic Ops ORT
• Traffic Portal
• Traffic Router
• Traffic Stats
• Traffic Vault
• unknown

Current behavior:

When making a GET request to api_capabilities with any of the following query parameters with values that do not exist:

• ?capability=DOESNTEXIST
• ?route=DOESNTEXIST
• ?id=100000000

Will return a null response:

HTTP\1.1 200 OK
{
    "response": null
}

Expected / new behavior:

Should return an empty array.

HTTP\1.1 200 OK
{
    "response": []
}

Minimal reproduction of the problem with instructions:

Anything else:

The capability query parameter is the only parameter that perl handled, and it would return an empty array. These other query parameters, should either be removed or should also return an empty array.

[mhoppa]

this was fixed in #4321 @mitchell852 @rawlinp @ocket8888 can you close