From 04fc14544a703a46a4a30f84b110a2742328734d Mon Sep 17 00:00:00 2001
From: Vadym Markov <markov.vadym@gmail.com>
Date: Sun, 4 Sep 2016 17:54:14 +0200
Subject: [PATCH] Add guard

---
 Source/SignalTracking/Units/InputSignalTracker.swift | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Source/SignalTracking/Units/InputSignalTracker.swift b/Source/SignalTracking/Units/InputSignalTracker.swift
index 2244821..240e0cf 100644
--- a/Source/SignalTracking/Units/InputSignalTracker.swift
+++ b/Source/SignalTracking/Units/InputSignalTracker.swift
@@ -68,6 +68,10 @@ public class InputSignalTracker: SignalTracker {
   }
 
   public func stop() {
+    guard audioEngine != nil else {
+      return
+    }
+
     audioEngine?.stop()
     audioEngine?.reset()
     audioEngine = nil