feat: some tuning to error messages and nil checks

Author: rodrigoscc

lua/nurl/actions.lua

@@ -114,10 +114,9 @@ M.builtin = {
     cancel = function(_)
         return function()
             local curl = vim.b.nurl_curl
-            local pid = curl.pid
 
-            if pid ~= nil then
-                local code, msg = uv.kill(pid, "sigterm")
+            if curl and curl.pid then
+                local code, msg = uv.kill(curl.pid, "sigterm")
                 if code ~= 0 then
                     vim.notify(
                         "Could not kill curl: " .. msg,

lua/nurl/environments.lua

@@ -56,7 +56,7 @@ local function create_coroutine()
     return coroutine.create(function()
         while true do
             if M.project_env_file == nil then
-                error("Environment file wasn't loaded. Stopping worker...")
+                error("Environment file wasn't loaded. Worker stopped.")
             end
 
             while #operations_queue == 0 do

lua/nurl/requests.lua

@@ -73,7 +73,7 @@ function M.expand(request, opts)
     assert(
         (request[1] and not request.url and type(request[1]) == "string")
             or (request.url and not request[1]),
-        "The request must have one and only one URL field"
+        "The request must have one and at most one URL field"
     )
 
     local super_url