Make sure appropriate defaults for omitted configs are used

src/mibew/libs/common/configurations.php

@@ -33,13 +33,19 @@ function load_system_configs()
     if (is_null($configs)) {
         $parser = new YamlParser();
         $configs = $parser->parse(file_get_contents(MIBEW_FS_ROOT . '/configs/config.yml'));
-        $configs += array(
-            // Mailer configs are not necessary and can be omited but the
-            // section must exist anyway.
-            'mailer' => array(),
-            // Cache section must extst too.
-            'cache' => array(),
-        );
+
+        // Mailer configs are not necessary and can be omited but the section
+        // must exist anyway. Empty statement is used to make sure null, false
+        // and "" will be converted to an empty array.
+        if (empty($configs['mailer'])) {
+            $configs['mailer'] = array();
+        }
+
+        // Cache section must extst too. The logic behind "empty" statement is
+        // the same as above.
+        if (empty($configs['cache'])) {
+            $configs['cache'] = array();
+        }
     }
 
     return $configs;