Add nil highlight (#71)

Author: hkupty

API.md

@@ -1,3 +1,6 @@
+format: using built-in markdown
+format: using built-in markdown
+format: discount not found, using markdown
 # acid.connections
 low-level connection handler
 

lua/acid/middlewares/virtualtext.lua

@@ -54,6 +54,8 @@ virtualtext.middleware = function(config)
           table.insert(vt, {data.out:gsub("\n", "\\n"), "String"})
       elseif data.value ~= nil and data.value ~= "nil" then
         table.insert(vt, {data.value, "Function"})
+      elseif data.value == "nil" then
+        table.insert(vt, {"nil", "Delimiter"})
       end
 
       if #vt > 0 then