diff --git a/examples/internal/clients/abe/api/swagger.yaml b/examples/internal/clients/abe/api/swagger.yaml
index 80a0ea203e2..a2686cf2b83 100644
--- a/examples/internal/clients/abe/api/swagger.yaml
+++ b/examples/internal/clients/abe/api/swagger.yaml
@@ -1864,11 +1864,9 @@ paths:
         in: "query"
         description: "The paths to update."
         required: false
-        type: "array"
-        items:
-          type: "string"
-        collectionFormat: "multi"
+        type: "string"
         x-exportParamName: "UpdateMask"
+        x-optionalDataType: "String"
       responses:
         200:
           description: "A successful response."
@@ -1910,11 +1908,9 @@ paths:
         in: "query"
         description: "The paths to update."
         required: false
-        type: "array"
-        items:
-          type: "string"
-        collectionFormat: "multi"
+        type: "string"
         x-exportParamName: "UpdateMask"
+        x-optionalDataType: "String"
       responses:
         200:
           description: "A successful response."
@@ -2620,10 +2616,8 @@ definitions:
       abe:
         $ref: "#/definitions/examplepbABitOfEverything"
       updateMask:
-        type: "array"
+        type: "string"
         description: "The paths to update."
-        items:
-          type: "string"
     title: "UpdateV2Request request for update includes the message and the update\
       \ mask"
   pathenumPathEnum:
diff --git a/examples/internal/clients/abe/api_a_bit_of_everything_service.go b/examples/internal/clients/abe/api_a_bit_of_everything_service.go
index c51a3ab96ad..45aaffd3dec 100644
--- a/examples/internal/clients/abe/api_a_bit_of_everything_service.go
+++ b/examples/internal/clients/abe/api_a_bit_of_everything_service.go
@@ -3554,13 +3554,13 @@ ABitOfEverythingServiceApiService
  * @param abeUuid
  * @param body
  * @param optional nil or *ABitOfEverythingServiceUpdateV2Opts - Optional Parameters:
-     * @param "UpdateMask" (optional.Interface of []string) -  The paths to update.
+     * @param "UpdateMask" (optional.String) -  The paths to update.
 
 @return interface{}
 */
 
 type ABitOfEverythingServiceUpdateV2Opts struct { 
-	UpdateMask optional.Interface
+	UpdateMask optional.String
 }
 
 func (a *ABitOfEverythingServiceApiService) ABitOfEverythingServiceUpdateV2(ctx context.Context, abeUuid string, body ExamplepbABitOfEverything, localVarOptionals *ABitOfEverythingServiceUpdateV2Opts) (interface{}, *http.Response, error) {
@@ -3581,7 +3581,7 @@ func (a *ABitOfEverythingServiceApiService) ABitOfEverythingServiceUpdateV2(ctx
 	localVarFormParams := url.Values{}
 
 	if localVarOptionals != nil && localVarOptionals.UpdateMask.IsSet() {
-		localVarQueryParams.Add("updateMask", parameterToString(localVarOptionals.UpdateMask.Value(), "multi"))
+		localVarQueryParams.Add("updateMask", parameterToString(localVarOptionals.UpdateMask.Value(), ""))
 	}
 	// to determine the Content-Type header
 	localVarHttpContentTypes := []string{"application/json", "application/x-foo-mime"}
@@ -3712,13 +3712,13 @@ ABitOfEverythingServiceApiService
  * @param abeUuid
  * @param body
  * @param optional nil or *ABitOfEverythingServiceUpdateV22Opts - Optional Parameters:
-     * @param "UpdateMask" (optional.Interface of []string) -  The paths to update.
+     * @param "UpdateMask" (optional.String) -  The paths to update.
 
 @return interface{}
 */
 
 type ABitOfEverythingServiceUpdateV22Opts struct { 
-	UpdateMask optional.Interface
+	UpdateMask optional.String
 }
 
 func (a *ABitOfEverythingServiceApiService) ABitOfEverythingServiceUpdateV22(ctx context.Context, abeUuid string, body ExamplepbABitOfEverything, localVarOptionals *ABitOfEverythingServiceUpdateV22Opts) (interface{}, *http.Response, error) {
@@ -3739,7 +3739,7 @@ func (a *ABitOfEverythingServiceApiService) ABitOfEverythingServiceUpdateV22(ctx
 	localVarFormParams := url.Values{}
 
 	if localVarOptionals != nil && localVarOptionals.UpdateMask.IsSet() {
-		localVarQueryParams.Add("updateMask", parameterToString(localVarOptionals.UpdateMask.Value(), "multi"))
+		localVarQueryParams.Add("updateMask", parameterToString(localVarOptionals.UpdateMask.Value(), ""))
 	}
 	// to determine the Content-Type header
 	localVarHttpContentTypes := []string{"application/json", "application/x-foo-mime"}
diff --git a/examples/internal/clients/abe/model_examplepb_update_v2_request.go b/examples/internal/clients/abe/model_examplepb_update_v2_request.go
index 2c867a542d0..dab839628b5 100644
--- a/examples/internal/clients/abe/model_examplepb_update_v2_request.go
+++ b/examples/internal/clients/abe/model_examplepb_update_v2_request.go
@@ -13,5 +13,5 @@ package abe
 type ExamplepbUpdateV2Request struct {
 	Abe *ExamplepbABitOfEverything `json:"abe,omitempty"`
 	// The paths to update.
-	UpdateMask []string `json:"updateMask,omitempty"`
+	UpdateMask string `json:"updateMask,omitempty"`
 }
diff --git a/examples/internal/clients/echo/api/swagger.yaml b/examples/internal/clients/echo/api/swagger.yaml
index c4221e8b272..cbda5f0f24b 100644
--- a/examples/internal/clients/echo/api/swagger.yaml
+++ b/examples/internal/clients/echo/api/swagger.yaml
@@ -433,11 +433,9 @@ paths:
       - name: "updateMask"
         in: "query"
         required: false
-        type: "array"
-        items:
-          type: "string"
-        collectionFormat: "multi"
+        type: "string"
         x-exportParamName: "UpdateMask"
+        x-optionalDataType: "String"
       responses:
         200:
           description: "A successful response."
@@ -468,16 +466,12 @@ definitions:
       body:
         $ref: "#/definitions/examplepbDynamicMessage"
       updateMask:
-        type: "array"
-        items:
-          type: "string"
+        type: "string"
     example:
       body:
         structField: "{}"
         valueField: "{}"
-      updateMask:
-      - "updateMask"
-      - "updateMask"
+      updateMask: "updateMask"
   examplepbEmbedded:
     type: "object"
     properties:
diff --git a/examples/internal/clients/echo/api_echo_service.go b/examples/internal/clients/echo/api_echo_service.go
index 0944bc92be4..1bcf461f765 100644
--- a/examples/internal/clients/echo/api_echo_service.go
+++ b/examples/internal/clients/echo/api_echo_service.go
@@ -933,13 +933,13 @@ EchoServiceApiService EchoPatch method receives a NonStandardUpdateRequest and r
  * @param ctx context.Context - for authentication, logging, cancellation, deadlines, tracing, etc. Passed from http.Request or context.Background().
  * @param body
  * @param optional nil or *EchoServiceEchoPatchOpts - Optional Parameters:
-     * @param "UpdateMask" (optional.Interface of []string) - 
+     * @param "UpdateMask" (optional.String) - 
 
 @return ExamplepbDynamicMessageUpdate
 */
 
 type EchoServiceEchoPatchOpts struct { 
-	UpdateMask optional.Interface
+	UpdateMask optional.String
 }
 
 func (a *EchoServiceApiService) EchoServiceEchoPatch(ctx context.Context, body ExamplepbDynamicMessage, localVarOptionals *EchoServiceEchoPatchOpts) (ExamplepbDynamicMessageUpdate, *http.Response, error) {
@@ -959,7 +959,7 @@ func (a *EchoServiceApiService) EchoServiceEchoPatch(ctx context.Context, body E
 	localVarFormParams := url.Values{}
 
 	if localVarOptionals != nil && localVarOptionals.UpdateMask.IsSet() {
-		localVarQueryParams.Add("updateMask", parameterToString(localVarOptionals.UpdateMask.Value(), "multi"))
+		localVarQueryParams.Add("updateMask", parameterToString(localVarOptionals.UpdateMask.Value(), ""))
 	}
 	// to determine the Content-Type header
 	localVarHttpContentTypes := []string{"application/json"}
diff --git a/examples/internal/clients/echo/model_examplepb_dynamic_message_update.go b/examples/internal/clients/echo/model_examplepb_dynamic_message_update.go
index cc7fb56195c..086ab7c045e 100644
--- a/examples/internal/clients/echo/model_examplepb_dynamic_message_update.go
+++ b/examples/internal/clients/echo/model_examplepb_dynamic_message_update.go
@@ -11,5 +11,5 @@ package echo
 
 type ExamplepbDynamicMessageUpdate struct {
 	Body *ExamplepbDynamicMessage `json:"body,omitempty"`
-	UpdateMask []string `json:"updateMask,omitempty"`
+	UpdateMask string `json:"updateMask,omitempty"`
 }
diff --git a/examples/internal/proto/examplepb/a_bit_of_everything.swagger.json b/examples/internal/proto/examplepb/a_bit_of_everything.swagger.json
index ede085b3308..148388b083f 100644
--- a/examples/internal/proto/examplepb/a_bit_of_everything.swagger.json
+++ b/examples/internal/proto/examplepb/a_bit_of_everything.swagger.json
@@ -2208,11 +2208,7 @@
             "description": "The paths to update.",
             "in": "query",
             "required": false,
-            "type": "array",
-            "items": {
-              "type": "string"
-            },
-            "collectionFormat": "multi"
+            "type": "string"
           }
         ],
         "tags": [
@@ -2272,11 +2268,7 @@
             "description": "The paths to update.",
             "in": "query",
             "required": false,
-            "type": "array",
-            "items": {
-              "type": "string"
-            },
-            "collectionFormat": "multi"
+            "type": "string"
           }
         ],
         "tags": [
@@ -3194,10 +3186,7 @@
           "$ref": "#/definitions/examplepbABitOfEverything"
         },
         "updateMask": {
-          "type": "array",
-          "items": {
-            "type": "string"
-          },
+          "type": "string",
           "description": "The paths to update."
         }
       },
diff --git a/examples/internal/proto/examplepb/echo_service.swagger.json b/examples/internal/proto/examplepb/echo_service.swagger.json
index 501cfc86152..80deb2a9a29 100644
--- a/examples/internal/proto/examplepb/echo_service.swagger.json
+++ b/examples/internal/proto/examplepb/echo_service.swagger.json
@@ -526,11 +526,7 @@
             "name": "updateMask",
             "in": "query",
             "required": false,
-            "type": "array",
-            "items": {
-              "type": "string"
-            },
-            "collectionFormat": "multi"
+            "type": "string"
           }
         ],
         "tags": [
@@ -559,10 +555,7 @@
           "$ref": "#/definitions/examplepbDynamicMessage"
         },
         "updateMask": {
-          "type": "array",
-          "items": {
-            "type": "string"
-          }
+          "type": "string"
         }
       }
     },