Logs: disable invalid upstream warning when api_backend is null and empty

Author: tkan145

CHANGELOG.md

@@ -39,6 +39,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 - Replace luafilesystem-ffi with [luafilesystem](https://github.com/lunarmodules/luafilesystem) [PR #1445](https://github.com/3scale/APIcast/pull/1445) [THREESCALE-10662](https://issues.redhat.com/browse/THREESCALE-10662)
 
+- Fix "Upstream cannot be null" error in APIcast logs [PR #1449](https://github.com/3scale/APIcast/pull/1449) [THREESCALE-5225](https://issues.redhat.com/browse/THREESCALE-5225)
+
 ### Added
 
 - Detect number of CPU shares when running on Cgroups V2 [PR #1410](https://github.com/3scale/apicast/pull/1410) [THREESCALE-10167](https://issues.redhat.com/browse/THREESCALE-10167)

gateway/src/apicast/proxy.lua

@@ -14,6 +14,7 @@ local Usage = require('apicast.usage')
 local errors = require('apicast.errors')
 local Upstream = require('apicast.upstream')
 local escape = require("resty.http.uri_escape")
+local cjson = require('cjson')
 
 local assert = assert
 local type = type
@@ -175,7 +176,8 @@ function _M.get_upstream(service, context)
 
   -- Due to API as a product, the api_backend is no longer needed because this
   -- can be handled by routing policy
-  if not service.api_backend then
+  local api_backend = service.api_backend
+  if not api_backend or api_backend == cjson.null or api_backend == '' then
     return nil, nil
   end
 

spec/proxy_spec.lua

@@ -1,5 +1,6 @@
 local http_ng_response = require('resty.http_ng.response')
 local lrucache = require('resty.lrucache')
+local cjson = require('cjson')
 
 local configuration_store = require 'apicast.configuration_store'
 local Service = require 'apicast.configuration.service'
@@ -64,6 +65,18 @@ describe('Proxy', function()
       assert.falsy(err)
     end)
 
+    it("on no api_backend return empty string and no error", function()
+      local upstream, err = get_upstream({api_backend = ''})
+      assert.falsy(upstream)
+      assert.falsy(err)
+    end)
+
+    it("on no api_backend return null and no error", function()
+      local upstream, err = get_upstream({api_backend = cjson.null})
+      assert.falsy(upstream)
+      assert.falsy(err)
+    end)
+
   end)
 
   describe('.authorize', function()