Derive mode from DSN function

- Add headers in all files
- Minor field name changes

src/Mapper/ExistsMapper.php

@@ -1,8 +1,15 @@
-<?php declare(strict_types=1);
+<?php
+/**
+ * @author Daniel J. Summers <daniel@bitbadger.solutions>
+ * @license MIT
+ */
+
+declare(strict_types=1);
 
 namespace BitBadger\PDODocument\Mapper;
 
-use BitBadger\PDODocument\{Configuration, DocumentException, Mode};
+use BitBadger\PDODocument\{Configuration, Mode};
+use Exception;
 
 /**
  * Map an EXISTS result to a boolean value
@@ -11,14 +18,13 @@ class ExistsMapper implements Mapper
 {
     /**
      * @inheritDoc
-     * @throws DocumentException If the database mode has not been set
+     * @throws Exception If the database mode has not been set
      */
     public function map(array $result): bool
     {
-        return match (Configuration::$mode) {
+        return match (Configuration::mode('map existence result')) {
             Mode::PgSQL  => (bool)$result[0],
-            Mode::SQLite => (int)$result[0] > 0,
-            default      => throw new DocumentException('Database mode not set; cannot map existence result'),
+            Mode::SQLite => (int)$result[0] > 0
         };
     }
 }