raise PublishXmlValidationError in validate workfile metadata

openpype/hosts/tvpaint/plugins/publish/help/validate_workfile_metadata.xml

@@ -0,0 +1,19 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<root>
+<error id="main">
+<title>Missing metadata</title>
+<description>## Your scene miss context metadata
+
+Your scene does not contain metadata about {missing_metadata}.
+
+### How to repair?
+
+Resave the scene using Workfiles tool or hit the "Repair" button on the right.
+</description>
+<detail>
+### How this could happend?
+
+You're using scene file that was not created using Workfiles tool.
+</detail>
+</error>
+</root>

openpype/hosts/tvpaint/plugins/publish/validate_workfile_metadata.py

@@ -1,5 +1,6 @@
 import pyblish.api
 from avalon.tvpaint import save_file
+from openpype.pipeline import PublishXmlValidationError
 
 
 class ValidateWorkfileMetadataRepair(pyblish.api.Action):
@@ -42,8 +43,12 @@ class ValidateWorkfileMetadata(pyblish.api.ContextPlugin):
                 missing_keys.append(key)
 
         if missing_keys:
-            raise AssertionError(
+            raise PublishXmlValidationError(
+                self,
                 "Current workfile is missing metadata about {}.".format(
                     ", ".join(missing_keys)
-                )
+                ),
+                formatting_data={
+                    "missing_metadata": ", ".join(missing_keys)
+                }
             )