Use of NULL in execlp() must have a pointer cast.

Signed-off-by: Kang-Che Sung <explorer09@gmail.com>

OpenFilesScreen.c

@@ -120,7 +120,9 @@ static OpenFiles_ProcessData* OpenFilesScreen_getProcessData(pid_t pid) {
       close(fdnull);
       char buffer[32] = {0};
       xSnprintf(buffer, sizeof(buffer), "%d", pid);
-      execlp("lsof", "lsof", "-P", "-o", "-p", buffer, "-F", NULL);
+      // Use of NULL in variadic functions must have a pointer cast.
+      // The NULL constant is not required by standard to have a pointer type.
+      execlp("lsof", "lsof", "-P", "-o", "-p", buffer, "-F", (char *)NULL);
       exit(127);
    }
    close(fdpair[1]);

TraceScreen.c

@@ -90,7 +90,9 @@ bool TraceScreen_forkTracer(TraceScreen* this) {
 
       char buffer[32] = {0};
       xSnprintf(buffer, sizeof(buffer), "%d", this->super.process->pid);
-      execlp("strace", "strace", "-T", "-tt", "-s", "512", "-p", buffer, NULL);
+      // Use of NULL in variadic functions must have a pointer cast.
+      // The NULL constant is not required by standard to have a pointer type.
+      execlp("strace", "strace", "-T", "-tt", "-s", "512", "-p", buffer, (char *)NULL);
 
       // Should never reach here, unless execlp fails ...
       const char* message = "Could not execute 'strace'. Please make sure it is available in your $PATH.";

linux/SystemdMeter.c

@@ -219,6 +219,8 @@ static void updateViaExec(void) {
          exit(1);
       dup2(fdnull, STDERR_FILENO);
       close(fdnull);
+      // Use of NULL in variadic functions must have a pointer cast.
+      // The NULL constant is not required by standard to have a pointer type.
       execlp("systemctl",
              "systemctl",
              "show",
@@ -227,7 +229,7 @@ static void updateViaExec(void) {
              "--property=NNames",
              "--property=NJobs",
              "--property=NInstalledJobs",
-             NULL);
+             (char *)NULL);
       exit(127);
    }
    close(fdpair[1]);