Add two new exceptions for invalid list values

exceptions/updates/MDInvalidColor.php

@@ -0,0 +1,26 @@
+<?PHP
+/**
+ * This file contains an exception class for usage of unaccepted color.
+ *
+ * @file
+ *
+ * @author Joshua Ramon Enslin <joshua@museum-digital.de>
+ */
+declare(strict_types = 1);
+
+/**
+ * Custom exception class to be raised when trying to use a color that is not
+ * accepted by museum-digital.
+ */
+final class MDInvalidColor extends MDgenericInvalidInputsException {
+    /**
+     * Error message.
+     *
+     * @return string
+     */
+    public function errorMessage() {
+        //error message
+        return 'The following color is not available: ' . $this->getMessage();
+
+    }
+}

exceptions/updates/MDInvalidObjectForm.php

@@ -0,0 +1,26 @@
+<?PHP
+/**
+ * This file contains an exception class for usage of unaccepted object form.
+ *
+ * @file
+ *
+ * @author Joshua Ramon Enslin <joshua@museum-digital.de>
+ */
+declare(strict_types = 1);
+
+/**
+ * Custom exception class to be raised when trying to use an object form that is not
+ * accepted by museum-digital.
+ */
+final class MDInvalidObjectForm extends MDgenericInvalidInputsException {
+    /**
+     * Error message.
+     *
+     * @return string
+     */
+    public function errorMessage() {
+        //error message
+        return 'The following object form is not available: ' . $this->getMessage();
+
+    }
+}