diff --git a/specification/eventgrid/Azure.Messaging.EventGrid.SystemEvents/Microsoft.ServiceBus/ServiceBus.tsp b/specification/eventgrid/Azure.Messaging.EventGrid.SystemEvents/Microsoft.ServiceBus/ServiceBus.tsp
index 0167548c82fe..d88bd7e74682 100644
--- a/specification/eventgrid/Azure.Messaging.EventGrid.SystemEvents/Microsoft.ServiceBus/ServiceBus.tsp
+++ b/specification/eventgrid/Azure.Messaging.EventGrid.SystemEvents/Microsoft.ServiceBus/ServiceBus.tsp
@@ -22,21 +22,24 @@ namespace Microsoft.EventGrid.SystemEvents {
 
   alias ServiceBusBaseEventData = {
     /** The namespace name of the Microsoft.ServiceBus resource. */
-    namespaceName?: string;
+    namespaceName: string;
 
     /** The endpoint of the Microsoft.ServiceBus resource. */
-    requestUri?: string;
+    requestUri: string;
 
     /** The entity type of the Microsoft.ServiceBus resource. Could be one of 'queue' or 'subscriber'. */
-    entityType?: string;
+    entityType: string;
 
     /** The name of the Microsoft.ServiceBus queue. If the entity type is of type 'subscriber', then this value will be null. */
-    queueName?: string;
+    #suppress "@azure-tools/typespec-azure-core/no-nullable" "Nullable backcompat with existing models"
+    queueName: string | null;
 
     /** The name of the Microsoft.ServiceBus topic. If the entity type is of type 'queue', then this value will be null. */
-    topicName?: string;
+    #suppress "@azure-tools/typespec-azure-core/no-nullable" "Nullable backcompat with existing models"
+    topicName: string | null;
 
     /** The name of the Microsoft.ServiceBus topic's subscription. If the entity type is of type 'queue', then this value will be null. */
-    subscriptionName?: string;
+    #suppress "@azure-tools/typespec-azure-core/no-nullable" "Nullable backcompat with existing models"
+    subscriptionName: string | null;
   };
 }
diff --git a/specification/eventgrid/data-plane/Microsoft.EventGrid/stable/2018-01-01/GeneratedSystemEvents.json b/specification/eventgrid/data-plane/Microsoft.EventGrid/stable/2018-01-01/GeneratedSystemEvents.json
index 72ff7ff8f974..668dd7440112 100644
--- a/specification/eventgrid/data-plane/Microsoft.EventGrid/stable/2018-01-01/GeneratedSystemEvents.json
+++ b/specification/eventgrid/data-plane/Microsoft.EventGrid/stable/2018-01-01/GeneratedSystemEvents.json
@@ -7013,17 +7013,28 @@
         },
         "queueName": {
           "type": "string",
-          "description": "The name of the Microsoft.ServiceBus queue. If the entity type is of type 'subscriber', then this value will be null."
+          "description": "The name of the Microsoft.ServiceBus queue. If the entity type is of type 'subscriber', then this value will be null.",
+          "x-nullable": true
         },
         "topicName": {
           "type": "string",
-          "description": "The name of the Microsoft.ServiceBus topic. If the entity type is of type 'queue', then this value will be null."
+          "description": "The name of the Microsoft.ServiceBus topic. If the entity type is of type 'queue', then this value will be null.",
+          "x-nullable": true
         },
         "subscriptionName": {
           "type": "string",
-          "description": "The name of the Microsoft.ServiceBus topic's subscription. If the entity type is of type 'queue', then this value will be null."
+          "description": "The name of the Microsoft.ServiceBus topic's subscription. If the entity type is of type 'queue', then this value will be null.",
+          "x-nullable": true
         }
-      }
+      },
+      "required": [
+        "namespaceName",
+        "requestUri",
+        "entityType",
+        "queueName",
+        "topicName",
+        "subscriptionName"
+      ]
     },
     "ServiceBusActiveMessagesAvailableWithNoListenersEventData": {
       "type": "object",
@@ -7043,17 +7054,28 @@
         },
         "queueName": {
           "type": "string",
-          "description": "The name of the Microsoft.ServiceBus queue. If the entity type is of type 'subscriber', then this value will be null."
+          "description": "The name of the Microsoft.ServiceBus queue. If the entity type is of type 'subscriber', then this value will be null.",
+          "x-nullable": true
         },
         "topicName": {
           "type": "string",
-          "description": "The name of the Microsoft.ServiceBus topic. If the entity type is of type 'queue', then this value will be null."
+          "description": "The name of the Microsoft.ServiceBus topic. If the entity type is of type 'queue', then this value will be null.",
+          "x-nullable": true
         },
         "subscriptionName": {
           "type": "string",
-          "description": "The name of the Microsoft.ServiceBus topic's subscription. If the entity type is of type 'queue', then this value will be null."
+          "description": "The name of the Microsoft.ServiceBus topic's subscription. If the entity type is of type 'queue', then this value will be null.",
+          "x-nullable": true
         }
-      }
+      },
+      "required": [
+        "namespaceName",
+        "requestUri",
+        "entityType",
+        "queueName",
+        "topicName",
+        "subscriptionName"
+      ]
     },
     "ServiceBusDeadletterMessagesAvailablePeriodicNotificationsEventData": {
       "type": "object",
@@ -7073,17 +7095,28 @@
         },
         "queueName": {
           "type": "string",
-          "description": "The name of the Microsoft.ServiceBus queue. If the entity type is of type 'subscriber', then this value will be null."
+          "description": "The name of the Microsoft.ServiceBus queue. If the entity type is of type 'subscriber', then this value will be null.",
+          "x-nullable": true
         },
         "topicName": {
           "type": "string",
-          "description": "The name of the Microsoft.ServiceBus topic. If the entity type is of type 'queue', then this value will be null."
+          "description": "The name of the Microsoft.ServiceBus topic. If the entity type is of type 'queue', then this value will be null.",
+          "x-nullable": true
         },
         "subscriptionName": {
           "type": "string",
-          "description": "The name of the Microsoft.ServiceBus topic's subscription. If the entity type is of type 'queue', then this value will be null."
+          "description": "The name of the Microsoft.ServiceBus topic's subscription. If the entity type is of type 'queue', then this value will be null.",
+          "x-nullable": true
         }
-      }
+      },
+      "required": [
+        "namespaceName",
+        "requestUri",
+        "entityType",
+        "queueName",
+        "topicName",
+        "subscriptionName"
+      ]
     },
     "ServiceBusDeadletterMessagesAvailableWithNoListenersEventData": {
       "type": "object",
@@ -7103,17 +7136,28 @@
         },
         "queueName": {
           "type": "string",
-          "description": "The name of the Microsoft.ServiceBus queue. If the entity type is of type 'subscriber', then this value will be null."
+          "description": "The name of the Microsoft.ServiceBus queue. If the entity type is of type 'subscriber', then this value will be null.",
+          "x-nullable": true
         },
         "topicName": {
           "type": "string",
-          "description": "The name of the Microsoft.ServiceBus topic. If the entity type is of type 'queue', then this value will be null."
+          "description": "The name of the Microsoft.ServiceBus topic. If the entity type is of type 'queue', then this value will be null.",
+          "x-nullable": true
         },
         "subscriptionName": {
           "type": "string",
-          "description": "The name of the Microsoft.ServiceBus topic's subscription. If the entity type is of type 'queue', then this value will be null."
+          "description": "The name of the Microsoft.ServiceBus topic's subscription. If the entity type is of type 'queue', then this value will be null.",
+          "x-nullable": true
         }
-      }
+      },
+      "required": [
+        "namespaceName",
+        "requestUri",
+        "entityType",
+        "queueName",
+        "topicName",
+        "subscriptionName"
+      ]
     },
     "SignalRServiceClientConnectionConnectedEventData": {
       "type": "object",
diff --git a/specification/eventgrid/data-plane/Microsoft.EventGrid/stable/2024-01-01/GeneratedSystemEvents.json b/specification/eventgrid/data-plane/Microsoft.EventGrid/stable/2024-01-01/GeneratedSystemEvents.json
index 4c447912b837..dafcc0a46a71 100644
--- a/specification/eventgrid/data-plane/Microsoft.EventGrid/stable/2024-01-01/GeneratedSystemEvents.json
+++ b/specification/eventgrid/data-plane/Microsoft.EventGrid/stable/2024-01-01/GeneratedSystemEvents.json
@@ -7141,17 +7141,28 @@
         },
         "queueName": {
           "type": "string",
-          "description": "The name of the Microsoft.ServiceBus queue. If the entity type is of type 'subscriber', then this value will be null."
+          "description": "The name of the Microsoft.ServiceBus queue. If the entity type is of type 'subscriber', then this value will be null.",
+          "x-nullable": true
         },
         "topicName": {
           "type": "string",
-          "description": "The name of the Microsoft.ServiceBus topic. If the entity type is of type 'queue', then this value will be null."
+          "description": "The name of the Microsoft.ServiceBus topic. If the entity type is of type 'queue', then this value will be null.",
+          "x-nullable": true
         },
         "subscriptionName": {
           "type": "string",
-          "description": "The name of the Microsoft.ServiceBus topic's subscription. If the entity type is of type 'queue', then this value will be null."
+          "description": "The name of the Microsoft.ServiceBus topic's subscription. If the entity type is of type 'queue', then this value will be null.",
+          "x-nullable": true
         }
-      }
+      },
+      "required": [
+        "namespaceName",
+        "requestUri",
+        "entityType",
+        "queueName",
+        "topicName",
+        "subscriptionName"
+      ]
     },
     "ServiceBusActiveMessagesAvailableWithNoListenersEventData": {
       "type": "object",
@@ -7171,17 +7182,28 @@
         },
         "queueName": {
           "type": "string",
-          "description": "The name of the Microsoft.ServiceBus queue. If the entity type is of type 'subscriber', then this value will be null."
+          "description": "The name of the Microsoft.ServiceBus queue. If the entity type is of type 'subscriber', then this value will be null.",
+          "x-nullable": true
         },
         "topicName": {
           "type": "string",
-          "description": "The name of the Microsoft.ServiceBus topic. If the entity type is of type 'queue', then this value will be null."
+          "description": "The name of the Microsoft.ServiceBus topic. If the entity type is of type 'queue', then this value will be null.",
+          "x-nullable": true
         },
         "subscriptionName": {
           "type": "string",
-          "description": "The name of the Microsoft.ServiceBus topic's subscription. If the entity type is of type 'queue', then this value will be null."
+          "description": "The name of the Microsoft.ServiceBus topic's subscription. If the entity type is of type 'queue', then this value will be null.",
+          "x-nullable": true
         }
-      }
+      },
+      "required": [
+        "namespaceName",
+        "requestUri",
+        "entityType",
+        "queueName",
+        "topicName",
+        "subscriptionName"
+      ]
     },
     "ServiceBusDeadletterMessagesAvailablePeriodicNotificationsEventData": {
       "type": "object",
@@ -7201,17 +7223,28 @@
         },
         "queueName": {
           "type": "string",
-          "description": "The name of the Microsoft.ServiceBus queue. If the entity type is of type 'subscriber', then this value will be null."
+          "description": "The name of the Microsoft.ServiceBus queue. If the entity type is of type 'subscriber', then this value will be null.",
+          "x-nullable": true
         },
         "topicName": {
           "type": "string",
-          "description": "The name of the Microsoft.ServiceBus topic. If the entity type is of type 'queue', then this value will be null."
+          "description": "The name of the Microsoft.ServiceBus topic. If the entity type is of type 'queue', then this value will be null.",
+          "x-nullable": true
         },
         "subscriptionName": {
           "type": "string",
-          "description": "The name of the Microsoft.ServiceBus topic's subscription. If the entity type is of type 'queue', then this value will be null."
+          "description": "The name of the Microsoft.ServiceBus topic's subscription. If the entity type is of type 'queue', then this value will be null.",
+          "x-nullable": true
         }
-      }
+      },
+      "required": [
+        "namespaceName",
+        "requestUri",
+        "entityType",
+        "queueName",
+        "topicName",
+        "subscriptionName"
+      ]
     },
     "ServiceBusDeadletterMessagesAvailableWithNoListenersEventData": {
       "type": "object",
@@ -7231,17 +7264,28 @@
         },
         "queueName": {
           "type": "string",
-          "description": "The name of the Microsoft.ServiceBus queue. If the entity type is of type 'subscriber', then this value will be null."
+          "description": "The name of the Microsoft.ServiceBus queue. If the entity type is of type 'subscriber', then this value will be null.",
+          "x-nullable": true
         },
         "topicName": {
           "type": "string",
-          "description": "The name of the Microsoft.ServiceBus topic. If the entity type is of type 'queue', then this value will be null."
+          "description": "The name of the Microsoft.ServiceBus topic. If the entity type is of type 'queue', then this value will be null.",
+          "x-nullable": true
         },
         "subscriptionName": {
           "type": "string",
-          "description": "The name of the Microsoft.ServiceBus topic's subscription. If the entity type is of type 'queue', then this value will be null."
+          "description": "The name of the Microsoft.ServiceBus topic's subscription. If the entity type is of type 'queue', then this value will be null.",
+          "x-nullable": true
         }
-      }
+      },
+      "required": [
+        "namespaceName",
+        "requestUri",
+        "entityType",
+        "queueName",
+        "topicName",
+        "subscriptionName"
+      ]
     },
     "SignalRServiceClientConnectionConnectedEventData": {
       "type": "object",