fix: honor optional request bodies during validation

src/validation.test.ts

@@ -497,6 +497,7 @@ describe.each([{}, { lazyCompileValidators: true }])('OpenAPIValidator with opts
                   operationId: 'createPet',
                   responses: { 200: { description: 'ok' } },
                   requestBody: {
+                    required: true,
                     content: {
                       'application/json': {
                         schema: petSchema,
@@ -519,6 +520,19 @@ describe.each([{}, { lazyCompileValidators: true }])('OpenAPIValidator with opts
                   },
                 },
               },
+              '/optional-pets': {
+                post: {
+                  operationId: 'createOptionalPet',
+                  responses: { 200: { description: 'ok' } },
+                  requestBody: {
+                    content: {
+                      'application/json': {
+                        schema: petSchema,
+                      },
+                    },
+                  },
+                },
+              },
               '/pets/schedule': {
                 post: {
                   operationId: 'createPetSchedule',
@@ -642,6 +656,27 @@ describe.each([{}, { lazyCompileValidators: true }])('OpenAPIValidator with opts
         expect(valid.errors && valid.errors[0].keyword).toBe('parse');
       });
 
+      test('passes validation when optional requestBody with one media type is omitted', async () => {
+        const valid = validator.validateRequest({
+          path: '/optional-pets',
+          method: 'post',
+          headers,
+        });
+        expect(valid.errors).toBeFalsy();
+      });
+
+      test('fails validation when optional requestBody with one media type is provided but invalid', async () => {
+        const valid = validator.validateRequest({
+          path: '/optional-pets',
+          method: 'post',
+          headers,
+          body: {
+            age: 40,
+          },
+        });
+        expect(valid.errors).toHaveLength(1);
+      });
+
       test('allows non-json data when application/json is not the only allowed media type', async () => {
         const valid = validator.validateRequest({
           path: '/pets',

src/validation.ts

@@ -578,8 +578,7 @@ export class OpenAPIValidator<D extends Document = Document> {
           },
         };
         requestBodySchema.required = [];
-        if (_.keys(requestBody.content).length === 1) {
-          // if application/json is the only specified format, it's required
+        if (requestBody.required) {
           requestBodySchema.required.push('requestBody');
         }