Canvas: Fix worker registration request schema

Make commit information optional and nullable

Change-Id: I181a7ac53f6b1618c11443b168af27e356922ace
diff --git a/apps/canvas/back/src/project_monitor.ts b/apps/canvas/back/src/project_monitor.ts
index 4b234a5..df20e05 100644
--- a/apps/canvas/back/src/project_monitor.ts
+++ b/apps/canvas/back/src/project_monitor.ts
@@ -22,12 +22,14 @@
 	address: z.string().url(),
 	status: z.optional(
 		z.object({
-			commit: z.optional(
-				z.object({
-					hash: z.string(),
-					message: z.string(),
-				}),
-			),
+			commit: z
+				.optional(
+					z.object({
+						hash: z.string(),
+						message: z.string(),
+					}),
+				)
+				.nullable(),
 			commands: z.optional(
 				z.array(
 					z.object({