Init limits if nil

transport.go

@@ -550,9 +550,14 @@
 				}
 				Logger.Printf("Sending %s failed with the following error: %s", eventType, string(b))
 			}
+
 			t.mu.Lock()
+			if t.limits == nil {
+				t.limits = make(ratelimit.Map)
+			}
 			t.limits.Merge(ratelimit.FromResponse(response))
 			t.mu.Unlock()
+
 			// Drain body up to a limit and close it, allowing the
 			// transport to reuse TCP connections.
 			_, _ = io.CopyN(io.Discard, response.Body, maxDrainResponseBytes)
@@ -690,6 +695,10 @@
 	}
 
 	t.mu.Lock()
+	if t.limits == nil {
+		t.limits = make(ratelimit.Map)
+	}
+
 	t.limits.Merge(ratelimit.FromResponse(response))
 	t.mu.Unlock()