Validate if any file sequences has been collected.

pype/plugins/global/publish/validate_filesequences.py

@@ -0,0 +1,12 @@
+import pyblish.api
+
+
+class ValidateFileSequences(pyblish.api.ContextPlugin):
+    """Validates whether any file sequences were collected."""
+
+    order = pyblish.api.ValidatorOrder
+    targets = ["filesequence"]
+    label = "Validate File Sequences"
+
+    def process(self, context):
+        assert context, "Nothing collected."