[monitoring-plugins] Change iritating NULL assignment

[RincewindsHat]

 Module: monitoring-plugins
 Branch: master
 Commit: c1c9abbfcafe8e55d86dfe13aed6874ad194d761
 Author: RincewindsHat <12514511+RincewindsHat at users.noreply.github.com>
   Date: Fri Dec 29 00:45:14 2023 +0100
    URL: https://www.monitoring-plugins.org/repositories/monitoring-plugins/commit/?id=c1c9abb

Change iritating NULL assignment

---

 plugins/popen.c  | 2 +-
 plugins/runcmd.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/plugins/popen.c b/plugins/popen.c
index 036bc60..54e63bc 100644
--- a/plugins/popen.c
+++ b/plugins/popen.c
@@ -105,7 +105,7 @@ spopen (const char *cmdstring)
 #endif
 
 	env[0] = strdup("LC_ALL=C");
-	env[1] = '\0';
+	env[1] = NULL;
 
 	/* if no command was passed, return with no error */
 	if (cmdstring == NULL)
diff --git a/plugins/runcmd.c b/plugins/runcmd.c
index 32fd6b9..ed49bb9 100644
--- a/plugins/runcmd.c
+++ b/plugins/runcmd.c
@@ -115,7 +115,7 @@ np_runcmd_open(const char *cmdstring, int *pfd, int *pfderr)
 	if(!np_pids) NP_RUNCMD_INIT;
 
 	env[0] = strdup("LC_ALL=C");
-	env[1] = '\0';
+	env[1] = NULL;
 
 	/* make copy of command string so strtok() doesn't silently modify it */
 	/* (the calling program may want to access it later) */