From 791be4766a07d0da7ee971ed57101114a77d3f04 Mon Sep 17 00:00:00 2001
From: LD <laurent.deru@gmail.com>
Date: Thu, 28 Nov 2019 23:37:33 +0100
Subject: [PATCH] MacOS: Don't crash if no elements are returned by
 IOHIDDeviceCopyMatchingElements

Fixes #797
---
 panda/src/device/ioKitInputDevice.cxx | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/panda/src/device/ioKitInputDevice.cxx b/panda/src/device/ioKitInputDevice.cxx
index 8468fd4816..1d8bf38f0f 100644
--- a/panda/src/device/ioKitInputDevice.cxx
+++ b/panda/src/device/ioKitInputDevice.cxx
@@ -114,12 +114,14 @@ IOKitInputDevice(IOHIDDeviceRef device) :
   }
 
   CFArrayRef elements = IOHIDDeviceCopyMatchingElements(device, nullptr, 0);
-  CFIndex count = CFArrayGetCount(elements);
-  for (CFIndex i = 0; i < count; ++i) {
-    IOHIDElementRef element = (IOHIDElementRef)CFArrayGetValueAtIndex(elements, i);
-    parse_element(element);
+  if (elements) {
+    CFIndex count = CFArrayGetCount(elements);
+    for (CFIndex i = 0; i < count; ++i) {
+      IOHIDElementRef element = (IOHIDElementRef)CFArrayGetValueAtIndex(elements, i);
+      parse_element(element);
+    }
+    CFRelease(elements);
   }
-  CFRelease(elements);
 
   if (_hat_element != nullptr) {
     _hat_left_button = (int)_buttons.size();