doc module: Add `DocEmptyException'

refs #4820

modules/doc/library/Doc/Exception/DocEmptyException.php

@@ -0,0 +1,12 @@
+<?php
+// {{{ICINGA_LICENSE_HEADER}}}
+// {{{ICINGA_LICENSE_HEADER}}}
+
+namespace Icinga\Module\Doc\Exception;
+
+/**
+ * Exception thrown if a documentation directory is empty
+ */
+class DocEmptyException extends DocException
+{
+}