Add new exception MDRequiredConfigNotSet for describing missing configs

exceptions/generic/MDRequiredConfigNotSet.php

@@ -0,0 +1,21 @@
+<?PHP
+declare(strict_types = 1);
+
+/**
+ * Custom exception class for errors loading configuration information.
+ */
+class MDRequiredConfigNotSet extends Exception {
+
+    /**
+     * Error message.
+     *
+     * @return string
+     */
+    public function errorMessage() {
+        //error message
+        $errorMsg = 'Could not connect to databse. Please try again later.';
+        return $errorMsg;
+
+    }
+
+}