backoffice: return a 404 on missing block (#55515)

tests/admin_pages/test_block.py

@@ -36,6 +36,14 @@ def teardown_module(module):
     clean_temporary_pub()
 
 
+def test_block_404(pub, blocks_feature):
+    create_superuser(pub)
+    create_role(pub)
+    BlockDef.wipe()
+    app = login(get_app(pub))
+    app.get('/backoffice/forms/blocks/1/', status=404)
+
+
 def test_block_new(pub, blocks_feature):
     create_superuser(pub)
     create_role(pub)

wcs/admin/blocks.py

@@ -24,6 +24,7 @@ from wcs.backoffice.snapshots import SnapshotsDirectory
 from wcs.blocks import BlockDef, BlockdefImportError
 from wcs.qommon import _, misc, template
 from wcs.qommon.backoffice.menu import html_top
+from wcs.qommon.errors import TraversalError
 from wcs.qommon.form import FileWidget, Form, HtmlWidget, StringWidget
 
 
@@ -198,7 +199,11 @@ class BlocksDirectory(Directory):
         return super()._q_traverse(path)
 
     def _q_lookup(self, component):
-        return BlockDirectory(self.section, BlockDef.get(component))
+        try:
+            block = BlockDef.get(component)
+        except KeyError:
+            raise TraversalError()
+        return BlockDirectory(self.section, block)
 
     def _q_index(self):
         html_top(self.section, title=_('Fields Blocks'))