use nil instead of empty string

config/config.exs

@@ -42,7 +42,7 @@ version = with {version, 0} <- System.cmd("git", ["rev-parse", "HEAD"]) do
 
 # Configures http settings, upstream proxy etc.
 config :pleroma, :http,
-  proxy_url: ""
+  proxy_url: nil
 
 config :pleroma, :instance,
   version: version,

lib/pleroma/http/http.ex

@@ -4,9 +4,9 @@ defmodule Pleroma.HTTP do
 
   def process_request_options(options) do
     config = Application.get_env(:pleroma, :http, [])
-    proxy = Keyword.get(config, :proxy_url, "")
+    proxy = Keyword.get(config, :proxy_url, nil)
     case proxy do
-      "" -> options
+      nil -> options
       _ -> options ++ [proxy: proxy]
     end
   end