In practice this is not always defined and should be treated as

optional, I think

client/src/schema/schema.ts

@@ -4564,7 +4564,7 @@ export interface components {
              * Changeset revision number
              * @description The linearized 0-based index of the changeset on the tool shed (0, 1, 2,...)
              */
-            ctx_rev: string;
+            ctx_rev?: string;
             /** Deleted */
             deleted: boolean;
             /** Dist To Shed */

lib/galaxy/schema/schema.py

@@ -2329,7 +2329,7 @@ class InstalledToolShedRepository(Model):
     owner: str = Field(title="Owner", description="Owner of repository")
     deleted: bool
     # This should be an int... but it would break backward compatiblity. Probably switch it at some point anyway?
-    ctx_rev: str = Field(
+    ctx_rev: Optional[str] = Field(
         title="Changeset revision number",
         description="The linearized 0-based index of the changeset on the tool shed (0, 1, 2,...)",
     )