Fixing #5467 - Cacti Log issues in certain circumstances

Cacti logging throws error when attempting to generate a log message from empty log string in PHP 8.x

CHANGELOG

@@ -76,6 +76,7 @@ Cacti CHANGELOG
 -issue#5459: There is no option to not duplicate Graph Template Data Query association when duplicating a Graph Template
 -issue#5460: When duplicating a Data Template errors can appear in the Cacti log
 -issue#5462: Package preview aparantely making changes to Cacti Templates or there is a Caching issue
+-issue#5467: Cacti logging throws error when attempting to generate a log message from empty log string in PHP 8.x
 -feature#5375: Add template for Fortinet firewall and Aruba Instant cluster
 -feature#5393: Add template for SNMP printer
 -feature#5418: Display device class before package import

lib/functions.php

@@ -210,7 +210,7 @@ function set_user_setting($config_name, $value, $user = -1) {
 		if (strlen($config_name) > 75) {
 			cacti_log("ERROR: User setting name '$config_name' is too long, will be truncated", false, 'SYSTEM');
 		}
-		
+
 		db_execute_prepared('REPLACE INTO settings_user
 			SET user_id = ?,
 			name = ?,
@@ -1280,6 +1280,10 @@ function cacti_log($string, $output = false, $environ = 'CMDPHP', $level = '') {
 		$database_log = false;
 	}
 
+	if (trim($string) == '') {
+		return false;
+	}
+
 	$last_log     = $database_log;
 	$database_log = false;
 	$force_level  = get_selective_log_level();
@@ -5086,8 +5090,13 @@ function mailer($from, $to, $cc, $bcc, $replyto, $subject, $body, $body_text = '
 	}
 
 	cacti_log($message, false, 'MAILER');
+
 	if ($result == false) {
-		cacti_log(cacti_debug_backtrace($rtype), false, 'MAILER');
+		$backtrace = trim(cacti_debug_backtrace($rtype));
+
+		if ($backtrace != '') {
+			cacti_log($backtrace, false, 'MAILER');
+		}
 	}
 
 	return $error;
@@ -7337,4 +7346,4 @@ function cacti_unserialize($strobj) {
 	} else {
 		return unserialize($strobj);
 	}
-}
+}