Add exception MDImporterDuplicateInvno

exceptions/updates/MDImporterDuplicateInvno.php

@@ -0,0 +1,29 @@
+<?PHP
+/**
+ * This exception is specific to the importer. It is to be returned if an object
+ * is to be imported while another of the same inventory number exists already -
+ * and where the import is set to only import new objects.
+ *
+ * @file
+ *
+ * @author Joshua Ramon Enslin <joshua@museum-digital.de>
+ */
+declare(strict_types = 1);
+
+/**
+ * This exception is specific to the importer. It is to be returned if an object
+ * is to be imported while another of the same inventory number exists already -
+ * and where the import is set to only import new objects.
+ */
+final class MDImporterDuplicateInvno extends MDgenericInvalidInputsException {
+    /**
+     * Error message.
+     *
+     * @return string
+     */
+    public function errorMessage() {
+        //error message
+        return 'This object already exists';
+
+    }
+}