Assign default data extension on discovered collection output

They used to be persisted as null in the database prior to this change.

lib/galaxy/model/store/discover.py

@@ -38,6 +38,10 @@
 from galaxy.util.hash_util import HASH_NAME_MAP
 
 if TYPE_CHECKING:
+    from galaxy.job_execution.output_collect import (
+        DatasetCollector,
+        ToolMetadataDatasetCollector,
+    )
     from galaxy.model.store import ModelExportStore
 
 log = logging.getLogger(__name__)
@@ -50,7 +54,7 @@ class MaxDiscoveredFilesExceededError(ValueError):
     pass
 
 
-CollectorT = Any  # TODO: setup an interface for these file collectors data classes.
+CollectorT = Union["DatasetCollector", "ToolMetadataDatasetCollector"]
 
 
 class ModelPersistenceContext(metaclass=abc.ABCMeta):
@@ -1056,19 +1060,21 @@ def name(self):
         return self.as_dict.get("name")
 
     @property
-    def dbkey(self):
-        return self.as_dict.get("dbkey", getattr(self.collector, "default_dbkey", "?"))
+    def dbkey(self) -> str:
+        return self.as_dict.get("dbkey", self.collector and self.collector.default_dbkey or "?")
 
     @property
-    def ext(self):
-        return self.as_dict.get("ext", getattr(self.collector, "default_ext", "data"))
+    def ext(self) -> str:
+        return self.as_dict.get("ext", self.collector and self.collector.default_ext or "data")
 
     @property
-    def visible(self):
+    def visible(self) -> bool:
         try:
             return self.as_dict["visible"].lower() == "visible"
         except KeyError:
-            return getattr(self.collector, "default_visible", True)
+            if self.collector and self.collector.default_visible is not None:
+                return self.collector.default_visible
+            return True
 
     @property
     def link_data(self):