Check if error logger available before using it

rebar.config

@@ -1,7 +1,7 @@
 %%% -*- mode: erlang; -*-
 {erl_opts, [debug_info]}.
 {deps, [
-        {worker_pool,   "2.1.0"}
+        {worker_pool,   "3.0.0"}
        ,{stillir, "1.0.0"}
        ]}.
 
@@ -18,7 +18,7 @@
  ,{test, [
           {deps, [
                   {lager, "3.2.1"}
-                 ,{meck, "0.8.4"}
+                 ,{meck, "0.8.10"}
                  ]}
          ]}
  ]}.

src/dogstatsd_vm_stats.erl

@@ -122,8 +122,13 @@ handle_info({timeout, R, ?TIMER_MSG}, S = #state{key=K, delay=D, timer_ref=R}) -
     dogstatsd:gauge([K,"run_queue"], erlang:statistics(run_queue), 1.00),
 
     %% Error logger backlog (lower is better)
-    {_, MQL} = process_info(whereis(error_logger), message_queue_len),
-    dogstatsd:gauge([K,"error_logger_queue_len"], MQL, 1.00),
+
+    case whereis(error_logger) of
+        undefined -> undefined;
+        Pid ->
+            {_, MQL} = process_info(Pid, message_queue_len),
+            dogstatsd:gauge([K,"error_logger_queue_len"], MQL, 1.00)
+    end,
 
     %% Memory usage. There are more options available, but not all were kept.
     %% Memory usage is in bytes.