added TemplatesSelectionError class

src/packme/Packman.py

@@ -8,6 +8,9 @@ from typing import Any, Dict, List, Optional
 
 from .PackerTemplate import PackerTemplate
 
+class TemplatesSelectionError(Exception):
+    pass
+
 class Packman:
     """This class implements the Packman engine for generating packer template json files and run packer optionally .
     """
@@ -59,6 +62,9 @@ class Packman:
         else:
             # Filter out the image names not present in the yaml file
             templates = [template for template in selected_templates if template in self._templates]
+            if not selected_templates:
+                raise TemplatesSelectionError("Empty templates selection")
+
 
         return templates