diff --git a/packages/core/src/getters/res-req-types.ts b/packages/core/src/getters/res-req-types.ts
index b1ad6d077..d01022c10 100644
--- a/packages/core/src/getters/res-req-types.ts
+++ b/packages/core/src/getters/res-req-types.ts
@@ -11,7 +11,7 @@ import {
 } from 'openapi3-ts/oas30';
 import { resolveObject } from '../resolvers/object';
 import { resolveExampleRefs, resolveRef } from '../resolvers/ref';
-import { ContextSpecs, ResReqTypesValue } from '../types';
+import { ContextSpecs, GeneratorImport, ResReqTypesValue } from '../types';
 import { camel } from '../utils';
 import { isReference } from '../utils/assertion';
 import { pascal } from '../utils/case';
@@ -95,6 +95,9 @@ export const getResReqTypes = (
                 ...context,
                 specKey: specKey || context.specKey,
               },
+              isRequestBodyOptional:
+                // Even though required is false by default, we only consider required to be false if specified. (See pull 1277)
+                'required' in bodySchema && bodySchema.required === false,
               isRef: true,
             })
           : undefined;
@@ -107,15 +110,25 @@ export const getResReqTypes = (
                 ...context,
                 specKey: specKey || context.specKey,
               },
+              isRequestBodyOptional:
+                'required' in bodySchema && bodySchema.required === false,
               isUrlEncoded: true,
               isRef: true,
             })
           : undefined;
 
+        const additionalImports = getFormDataAdditionalImports({
+          schemaObject: mediaType?.schema,
+          context: {
+            ...context,
+            specKey: specKey || context.specKey,
+          },
+        });
+
         return [
           {
             value: name,
-            imports: [{ name, specKey, schemaName }],
+            imports: [{ name, specKey, schemaName }, ...additionalImports],
             schemas: [],
             type: 'unknown',
             isEnum: false,
@@ -170,6 +183,8 @@ export const getResReqTypes = (
                   name: propName,
                   schemaObject: mediaType.schema!,
                   context,
+                  isRequestBodyOptional:
+                    'required' in res && res.required === false,
                 })
               : undefined;
 
@@ -179,12 +194,18 @@ export const getResReqTypes = (
                   schemaObject: mediaType.schema!,
                   context,
                   isUrlEncoded: true,
+                  isRequestBodyOptional:
+                    'required' in res && res.required === false,
                 })
               : undefined;
 
+            const additionalImports = getFormDataAdditionalImports({
+              schemaObject: mediaType.schema!,
+              context,
+            });
             return {
               ...resolvedValue,
-              imports: resolvedValue.imports,
+              imports: [...resolvedValue.imports, ...additionalImports],
               formData,
               formUrlEncoded,
               contentType,
@@ -220,23 +241,47 @@ export const getResReqTypes = (
   );
 };
 
+const getFormDataAdditionalImports = ({
+  schemaObject,
+  context,
+}: {
+  schemaObject: SchemaObject | ReferenceObject;
+  context: ContextSpecs;
+}): GeneratorImport[] => {
+  const { schema } = resolveRef<SchemaObject>(schemaObject, context);
+  if (schema.type === 'object') {
+    if (schema.oneOf || schema.anyOf) {
+      const combinedSchemas = schema.oneOf || schema.anyOf;
+
+      return combinedSchemas!.map((schema) => {
+        const { imports } = resolveRef<SchemaObject>(schema, context);
+        return imports[0];
+      });
+    }
+  }
+  return [];
+};
+
 const getSchemaFormDataAndUrlEncoded = ({
   name,
   schemaObject,
   context,
+  isRequestBodyOptional,
   isUrlEncoded,
   isRef,
 }: {
   name: string;
   schemaObject: SchemaObject | ReferenceObject;
   context: ContextSpecs;
+  isRequestBodyOptional: boolean;
   isUrlEncoded?: boolean;
   isRef?: boolean;
-}) => {
+}): string => {
   const { schema, imports } = resolveRef<SchemaObject>(schemaObject, context);
   const propName = camel(
     !isRef && isReference(schemaObject) ? imports[0].name : name,
   );
+  const additionalImports: GeneratorImport[] = [];
 
   const variableName = isUrlEncoded ? 'formUrlEncoded' : 'formData';
   let form = isUrlEncoded
@@ -256,12 +301,24 @@ const getSchemaFormDataAndUrlEncoded = ({
             context,
           );
 
-          return resolveSchemaPropertiesToFormData({
-            schema: combinedSchema,
-            variableName,
-            propName: shouldCast ? `(${propName} as any)` : propName,
-            context,
-          });
+          if (shouldCast) additionalImports.push(imports[0]);
+
+          const newPropName = shouldCast
+            ? `${propName}${pascal(imports[0].name)}`
+            : propName;
+          const newPropDefinition = shouldCast
+            ? `const ${newPropName} = (${propName} as ${imports[0].name}${isRequestBodyOptional ? ' | undefined' : ''});\n`
+            : '';
+          return (
+            newPropDefinition +
+            resolveSchemaPropertiesToFormData({
+              schema: combinedSchema,
+              variableName,
+              propName: newPropName,
+              context,
+              isRequestBodyOptional,
+            })
+          );
         })
         .filter((x) => x)
         .join('\n');
@@ -275,6 +332,7 @@ const getSchemaFormDataAndUrlEncoded = ({
         variableName,
         propName,
         context,
+        isRequestBodyOptional,
       });
 
       form += formDataValues;
@@ -303,11 +361,13 @@ const resolveSchemaPropertiesToFormData = ({
   variableName,
   propName,
   context,
+  isRequestBodyOptional,
 }: {
   schema: SchemaObject;
   variableName: string;
   propName: string;
   context: ContextSpecs;
+  isRequestBodyOptional: boolean;
 }) => {
   const formDataValues = Object.entries(schema.properties ?? {}).reduce(
     (acc, [key, value]) => {
@@ -315,27 +375,34 @@ const resolveSchemaPropertiesToFormData = ({
 
       let formDataValue = '';
 
-      const formatedKey = !keyword.isIdentifierNameES5(key)
+      const formattedKeyPrefix = !isRequestBodyOptional
+        ? ''
+        : !keyword.isIdentifierNameES5(key)
+          ? '?.'
+          : '?';
+      const formattedKey = !keyword.isIdentifierNameES5(key)
         ? `['${key}']`
         : `.${key}`;
 
-      const valueKey = `${propName}${formatedKey}`;
+      const valueKey = `${propName}${formattedKeyPrefix}${formattedKey}`;
+      const nonOptionalValueKey = `${propName}${formattedKey}`;
 
       if (property.type === 'object') {
-        formDataValue = `${variableName}.append('${key}', JSON.stringify(${valueKey}));\n`;
+        formDataValue = `${variableName}.append('${key}', JSON.stringify(${nonOptionalValueKey}));\n`;
       } else if (property.type === 'array') {
-        formDataValue = `${valueKey}.forEach(value => ${variableName}.append('${key}', value));\n`;
+        formDataValue = `${nonOptionalValueKey}.forEach(value => ${variableName}.append('${key}', value));\n`;
       } else if (
         property.type === 'number' ||
         property.type === 'integer' ||
         property.type === 'boolean'
       ) {
-        formDataValue = `${variableName}.append('${key}', ${valueKey}.toString())\n`;
+        formDataValue = `${variableName}.append('${key}', ${nonOptionalValueKey}.toString())\n`;
       } else {
-        formDataValue = `${variableName}.append('${key}', ${valueKey})\n`;
+        formDataValue = `${variableName}.append('${key}', ${nonOptionalValueKey})\n`;
       }
 
-      const isRequired = schema.required?.includes(key);
+      const isRequired =
+        schema.required?.includes(key) && !isRequestBodyOptional;
 
       if (property.nullable) {
         if (isRequired) {
@@ -344,7 +411,7 @@ const resolveSchemaPropertiesToFormData = ({
 
         return (
           acc +
-          `if(${valueKey} !== undefined && ${valueKey} !== null) {\n ${formDataValue} }\n`
+          `if(${valueKey} !== undefined && ${nonOptionalValueKey} !== null) {\n ${formDataValue} }\n`
         );
       }
 
diff --git a/tests/configs/swr.config.ts b/tests/configs/swr.config.ts
index a8e659afd..4efa0a6fc 100644
--- a/tests/configs/swr.config.ts
+++ b/tests/configs/swr.config.ts
@@ -203,4 +203,18 @@ export default defineConfig({
       },
     },
   },
+  formData: {
+    output: {
+      target: '../generated/swr/form-data-optional-request/endpoints.ts',
+      schemas: '../generated/swr/form-data-optional-request/model',
+      client: 'swr',
+      mock: true,
+    },
+    input: {
+      target: '../specifications/form-data-optional-request.yaml',
+      override: {
+        transformer: '../transformers/add-version.js',
+      },
+    },
+  },
 });
diff --git a/tests/specifications/form-data-optional-request.yaml b/tests/specifications/form-data-optional-request.yaml
new file mode 100644
index 000000000..a1a81e9c6
--- /dev/null
+++ b/tests/specifications/form-data-optional-request.yaml
@@ -0,0 +1,90 @@
+openapi: '3.0.0'
+info:
+  version: 1.0.0
+  title: Swagger Petstore
+  license:
+    name: MIT
+servers:
+  - url: http://petstore.swagger.io/v1
+paths:
+  /pets:
+    post:
+      summary: Create a pet
+      operationId: createPets
+      tags:
+        - pets
+      requestBody:
+        required: false
+        content:
+          multipart/form-data:
+            schema:
+              $ref: '#/components/schemas/Pet'
+      responses:
+        '200':
+          description: Created Pet
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/Pet'
+        default:
+          description: unexpected error
+          content:
+            application/json:
+              schema:
+                $ref: '#/components/schemas/Error'
+components:
+  schemas:
+    Pet:
+      type: object
+      oneOf:
+        - $ref: '#/components/schemas/PetBase'
+        - $ref: '#/components/schemas/PetExtended'
+      required:
+        - id
+        - name
+      properties:
+        '@id':
+          type: string
+          format: iri-reference
+        email:
+          type: string
+          format: email
+        callingCode:
+          type: string
+          enum: ['+33', '+420', '+33'] # intentional duplicated value
+        country:
+          type: string
+          enum: ["People's Republic of China", 'Uruguay']
+    Error:
+      type: object
+      required:
+        - code
+        - message
+      properties:
+        code:
+          type: integer
+          format: int32
+        message:
+          type: string
+
+    PetBase:
+      type: object
+      required:
+        - name
+      properties:
+        name:
+          type: string
+        tag:
+          type: string
+    PetExtended:
+      type: object
+      required:
+        - name
+      properties:
+        id:
+          type: integer
+          format: int64
+        name:
+          type: string
+        tag:
+          type: string