fix(apigateway): Explicitly test for undefined instead of falsey for stage default options (#20868)

Fixes #20860

Default options for throttling burst and rate limits could be interpreted incorrectly as undefined if they were set to zero. 

----

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Author: flemjame-at-amazon

packages/@aws-cdk/aws-apigateway/lib/stage.ts

@@ -310,7 +310,7 @@ export class Stage extends Resource implements IStage {
     };
 
     // if any of them are defined, add an entry for '/*/*'.
-    const hasCommonOptions = Object.keys(commonMethodOptions).map(v => (commonMethodOptions as any)[v]).filter(x => x).length > 0;
+    const hasCommonOptions = Object.keys(commonMethodOptions).map(v => (commonMethodOptions as any)[v]).filter(x => x !== undefined).length > 0;
     if (hasCommonOptions) {
       settings.push(renderEntry('/*/*', commonMethodOptions));
     }

packages/@aws-cdk/aws-apigateway/test/stage.test.ts

@@ -2,6 +2,7 @@ import { Template } from '@aws-cdk/assertions';
 import * as logs from '@aws-cdk/aws-logs';
 import * as cdk from '@aws-cdk/core';
 import * as apigateway from '../lib';
+import { ApiDefinition } from '../lib';
 
 describe('stage', () => {
   test('minimal setup', () => {
@@ -396,4 +397,30 @@ describe('stage', () => {
       accessLogFormat: testFormat,
     })).toThrow(/Access log format is specified without a destination/);
   });
+
+  test('default throttling settings', () => {
+    // GIVEN
+    const stack = new cdk.Stack();
+    new apigateway.SpecRestApi(stack, 'testapi', {
+      apiDefinition: ApiDefinition.fromInline({
+        openapi: '3.0.2',
+      }),
+      deployOptions: {
+        throttlingBurstLimit: 0,
+        throttlingRateLimit: 0,
+        metricsEnabled: false,
+      },
+    });
+
+    // THEN
+    Template.fromStack(stack).hasResourceProperties('AWS::ApiGateway::Stage', {
+      MethodSettings: [{
+        DataTraceEnabled: false,
+        HttpMethod: '*',
+        ResourcePath: '/*',
+        ThrottlingBurstLimit: 0,
+        ThrottlingRateLimit: 0,
+      }],
+    });
+  });
 });