refactor: remove inappropriate default values

These are the values for MySQLi.

Author: kenjis

phpstan-baseline.php

@@ -3168,7 +3168,7 @@
 ];
 $ignoreErrors[] = [
 	'message' => '#^Construct empty\\(\\) is not allowed\\. Use more strict comparison\\.$#',
-	'count' => 6,
+	'count' => 4,
 	'path' => __DIR__ . '/system/Database/MySQLi/Forge.php',
 ];
 $ignoreErrors[] = [

system/Database/BaseConnection.php

@@ -144,7 +144,7 @@ abstract class BaseConnection implements ConnectionInterface
      *
      * @var string
      */
-    protected $charset = 'utf8mb4';
+    protected $charset = '';
 
     /**
      * Collation
@@ -153,7 +153,7 @@ abstract class BaseConnection implements ConnectionInterface
      *
      * @var string
      */
-    protected $DBCollat = 'utf8mb4_general_ci';
+    protected $DBCollat = '';
 
     /**
      * Swap Prefix

system/Database/MySQLi/Forge.php

@@ -116,11 +116,11 @@ protected function _createTableAttributes(array $attributes): string
             }
         }
 
-        if (! empty($this->db->charset) && ! strpos($sql, 'CHARACTER SET') && ! strpos($sql, 'CHARSET')) {
+        if ($this->db->charset !== '' && ! strpos($sql, 'CHARACTER SET') && ! strpos($sql, 'CHARSET')) {
             $sql .= ' DEFAULT CHARACTER SET = ' . $this->db->escapeString($this->db->charset);
         }
 
-        if (! empty($this->db->DBCollat) && ! strpos($sql, 'COLLATE')) {
+        if ($this->db->DBCollat !== '' && ! strpos($sql, 'COLLATE')) {
             $sql .= ' COLLATE = ' . $this->db->escapeString($this->db->DBCollat);
         }