NullReferenceException when Content-type unspecified.

[AKomyshan]

For reproduce this error you simply can run Getting started example.

In current version we must set Content-type for all requests, but in case of GET methods when we produce request from browser Content-type are not added to headers request.

I have research the HTTP Protocol specification and googling should we set Content-type for all requests and TL;DR: Get requests should not have content-type because they do not have request entity (that is, a body)

I suggest to make the Content-type is not required. (At least for GET requests)

Repro steps:

1. Run https://functionmonkey.azurefromthetrenches.com/guides/gettingStarted.html this guide.
2. Run HelloWorld function from browser.

Error example:

` Http Functions:

    HelloWorldProxy: [GET] http://localhost:7071/api/v1/HelloWorld

    HelloWorld: [GET] http://localhost:7071/api/HelloWorld

[01.02.2019 11:01:10] Executing HTTP request: {
[01.02.2019 11:01:10]   "requestId": "db8c0b57-3857-4c51-b99b-778140cf5f63",
[01.02.2019 11:01:10]   "method": "GET",
[01.02.2019 11:01:10]   "uri": "/api/v1/HelloWorld"
[01.02.2019 11:01:10] }
[01.02.2019 11:01:11] Executing 'Functions.HelloWorldProxy' (Reason='This function was programmatically called via the host APIs.', Id=796ca58c-035e-41ee-ad26-ae9464a70c2c)
[01.02.2019 11:01:11] Host lock lease acquired by instance ID '00000000000000000000000011CD3113'.
[01.02.2019 11:01:11] Executing request via Azure Function Proxies
[01.02.2019 11:01:11] Executing 'HelloWorld' (Reason='This function was programmatically called via the host APIs.', Id=7e582cfa-c725-4dc0-933b-4b742d30ac1b)
[01.02.2019 11:01:12] HTTP trigger function HelloWorld processed a request.
[01.02.2019 11:01:16] Executed 'HelloWorld' (Failed, Id=7e582cfa-c725-4dc0-933b-4b742d30ac1b)

[01.02.2019 11:01:16] System.Private.CoreLib: Exception while executing function: HelloWorld. TestNRE.Functions.dll: Object reference not set to an instance of an object.

[01.02.2019 11:01:16] Executed 'Functions.HelloWorldProxy' (Succeeded, Id=796ca58c-035e-41ee-ad26-ae9464a70c2c)
[01.02.2019 11:01:17] Executed HTTP request: {
[01.02.2019 11:01:17]   "requestId": "db8c0b57-3857-4c51-b99b-778140cf5f63",
[01.02.2019 11:01:17]   "method": "GET",
[01.02.2019 11:01:17]   "uri": "/api/v1/HelloWorld",
[01.02.2019 11:01:17]   "identities": [
[01.02.2019 11:01:17]     {
[01.02.2019 11:01:17]       "type": "WebJobsAuthLevel",
[01.02.2019 11:01:17]       "level": "Admin"
[01.02.2019 11:01:17]     }
[01.02.2019 11:01:17]   ],
[01.02.2019 11:01:17]   "status": 500,
[01.02.2019 11:01:17]   "duration": 6194
[01.02.2019 11:01:17] }`

Error reason:

Looks like trouble in http.csharp.handlebars file in line
string contentType = req.ContentType.ToLower();

UPD: I can suggest a PR to fix this bug, but I don't have permissions to push.

[JamesRandall]

Thanks for reporting this in such a clear way - super appreciated.

I happened to be in the code resolving a Swagger issue so have made this fix while there. Should be in FunctionMonkey.Compiler 0.19.3.

Thank you!