Ensure that "memstring2bytes" can handle if an empty or value with no number is passed in

src/Core/Convert.php

@@ -451,6 +451,10 @@ class Convert
         // Remove non-numeric characters from the size
         $size = preg_replace('/[^0-9\.\-]/', '', $memString ?? '');
 
+        if (empty($size)) {
+            return 0;
+        }
+
         if ($unit) {
             // Find the position of the unit in the ordered string which is the power
             // of magnitude to multiply a kilobyte by

tests/php/Core/ConvertTest.php

@@ -437,7 +437,10 @@ PHP
             'mbytes' => ['512 mbytes', 512 * 1024 * 1024],
             'megabytes' => ['512 megabytes', 512 * 1024 * 1024],
             'giga' => ['1024g', 1024 * 1024 * 1024 * 1024],
-            'G' => ['1024G', 1024 * 1024 * 1024 * 1024]
+            'G' => ['1024G', 1024 * 1024 * 1024 * 1024],
+            'blank' => ['', 0],
+            'null' => [null, 0],
+            'no_numbers' => ['k', 0],
         ];
     }
 
@@ -459,6 +462,7 @@ PHP
     public function bytes2MemStringProvider()
     {
         return [
+            [0, '0B'],
             [200, '200B'],
             [2 * 1024, '2K'],
             [512 * 1024 * 1024, '512M'],