From 2220e497bda8b274677e660fb5922cbb31487235 Mon Sep 17 00:00:00 2001
From: Guy McSwain <guy.mcswain@gmail.com>
Date: Fri, 18 Dec 2020 20:23:52 -0600
Subject: [PATCH] Fix issue#397 gpioSetTimerFunc NULL cancel error

---
 pigpio.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/pigpio.c b/pigpio.c
index 9428b71..af94c11 100644
--- a/pigpio.c
+++ b/pigpio.c
@@ -12488,8 +12488,11 @@ int gpioSetTimerFunc(unsigned id, unsigned millis, gpioTimerFunc_t f)
    if (id > PI_MAX_TIMER)
       SOFT_ERROR(PI_BAD_TIMER, "bad timer id (%d)", id);
 
-   if ((millis < PI_MIN_MS) || (millis > PI_MAX_MS))
-      SOFT_ERROR(PI_BAD_MS, "timer %d, bad millis (%d)", id, millis);
+   if (f)
+   {
+      if ((millis < PI_MIN_MS) || (millis > PI_MAX_MS))
+         SOFT_ERROR(PI_BAD_MS, "timer %d, bad millis (%d)", id, millis);
+   }
 
    intGpioSetTimerFunc(id, millis, f, 0, NULL);