completed most of 05 ticket v2

exercises/05_ticket_v2/05_nullability/src/lib.rs

@@ -36,7 +36,10 @@ impl Ticket {
         }
     }
     pub fn assigned_to(&self) -> Option<&String> {
-        todo!()
+        let Status::InProgress { assigned_to } = &self.status else {
+            return None;
+        };
+        Some(assigned_to)
     }
 }