diff --git a/lib/mobile/mobile.class.php b/lib/mobile/mobile.class.php
index a5ef550e72..f7f6d5eeff 100644
--- a/lib/mobile/mobile.class.php
+++ b/lib/mobile/mobile.class.php
@@ -218,7 +218,7 @@ class mobile
         'iPad'              => 'iPad|iPad.*Mobile',
         // Removed |^.*Android.*Nexus(?!(?:Mobile).)*$
         // @see #442
-        'NexusTablet'       => 'Android.*Nexus[\s]+(7|9|10)', 
+        'NexusTablet'       => 'Android.*Nexus[\s]+(7|9|10)',
         'SamsungTablet'     => 'SAMSUNG.*Tablet|Galaxy.*Tab|SC-01C|GT-P1000|GT-P1003|GT-P1010|GT-P3105|GT-P6210|GT-P6800|GT-P6810|GT-P7100|GT-P7300|GT-P7310|GT-P7500|GT-P7510|SCH-I800|SCH-I815|SCH-I905|SGH-I957|SGH-I987|SGH-T849|SGH-T859|SGH-T869|SPH-P100|GT-P3100|GT-P3108|GT-P3110|GT-P5100|GT-P5110|GT-P6200|GT-P7320|GT-P7511|GT-N8000|GT-P8510|SGH-I497|SPH-P500|SGH-T779|SCH-I705|SCH-I915|GT-N8013|GT-P3113|GT-P5113|GT-P8110|GT-N8010|GT-N8005|GT-N8020|GT-P1013|GT-P6201|GT-P7501|GT-N5100|GT-N5105|GT-N5110|SHV-E140K|SHV-E140L|SHV-E140S|SHV-E150S|SHV-E230K|SHV-E230L|SHV-E230S|SHW-M180K|SHW-M180L|SHW-M180S|SHW-M180W|SHW-M300W|SHW-M305W|SHW-M380K|SHW-M380S|SHW-M380W|SHW-M430W|SHW-M480K|SHW-M480S|SHW-M480W|SHW-M485W|SHW-M486W|SHW-M500W|GT-I9228|SCH-P739|SCH-I925|GT-I9200|GT-P5200|GT-P5210|GT-P5210X|SM-T311|SM-T310|SM-T310X|SM-T210|SM-T210R|SM-T211|SM-P600|SM-P601|SM-P605|SM-P900|SM-P901|SM-T217|SM-T217A|SM-T217S|SM-P6000|SM-T3100|SGH-I467|XE500|SM-T110|GT-P5220|GT-I9200X|GT-N5110X|GT-N5120|SM-P905|SM-T111|SM-T2105|SM-T315|SM-T320|SM-T320X|SM-T321|SM-T520|SM-T525|SM-T530NU|SM-T230NU|SM-T330NU|SM-T900|XE500T1C|SM-P605V|SM-P905V|SM-T337V|SM-T537V|SM-T707V|SM-T807V|SM-P600X|SM-P900X|SM-T210X|SM-T230|SM-T230X|SM-T325|GT-P7503|SM-T531|SM-T330|SM-T530|SM-T705|SM-T705C|SM-T535|SM-T331|SM-T800|SM-T700|SM-T537|SM-T807|SM-P907A|SM-T337A|SM-T537A|SM-T707A|SM-T807A|SM-T237|SM-T807P|SM-P607T|SM-T217T|SM-T337T|SM-T807T|SM-T116NQ|SM-P550|SM-T350|SM-T550|SM-T9000|SM-P9000|SM-T705Y|SM-T805|GT-P3113|SM-T710|SM-T810|SM-T815|SM-T360|SM-T533|SM-T113|SM-T335|SM-T715', // SCH-P709|SCH-P729|SM-T2558|GT-I9205 - Samsung Mega - treat them like a regular phone.
         // http://docs.aws.amazon.com/silk/latest/developerguide/user-agent.html
         'Kindle'            => 'Kindle|Silk.*Accelerated|Android.*\b(KFOT|KFTT|KFJWI|KFJWA|KFOTE|KFSOWI|KFTHWI|KFTHWA|KFAPWI|KFAPWA|WFJWAE|KFSAWA|KFSAWI|KFASWI)\b',
@@ -756,11 +756,11 @@ class mobile
         return self::$uaHttpHeaders;
     }
 
-    
+
     /**
      * Set CloudFront headers
      * http://docs.aws.amazon.com/AmazonCloudFront/latest/DeveloperGuide/header-caching.html#header-caching-web-device
-     * 
+     *
      * @param array $cfHeaders List of HTTP headers
      *
      * @return  boolean If there were CloudFront headers to be set
@@ -1213,7 +1213,7 @@ class mobile
      */
     public function match($regex, $userAgent = null)
     {
-        $match = (bool) preg_match(sprintf('#%s#is', $regex), (false === empty($userAgent) ? $userAgent : $this->userAgent), $matches);
+        $match = (bool) preg_match(sprintf('#%s#is', $regex), (false === empty($userAgent) ? $userAgent : ($this->userAgent ? $this->userAgent : '')), $matches);
         // If positive match is found, store the results for debug.
         if ($match) {
             $this->matchingRegex = $regex;