Args decorator try to read property of undefined

[techo207]

Describe the Bug
I'm not sure if it is a bug, or my specific use case.
I'm creating a custom decorator that inject a generic find function as field function in the ObjectType class. to achive it i'm using the Args decorator as a function but it throws a error in runtine.

Cannot read property '0' of undefined

To Reproduce

@ArgsType()
class Ca{
   @Field(() => String)
   a: string;
}

@ObjectType()
class A {
    @ConnectionField( () => ProductFindArgs )
    prueba;
}

export function ConnectionField( findArgs: any, options?: FieldOptions ) {
	return function ConnectionDecorator( target: any, propertyKey: string | symbol ) {
		const newPropertyName = `_${String( propertyKey )}Connection`;
		const field = Field( () => String , { name: String( propertyKey ) } );
		const args = Args(findArgs);
		target[newPropertyName] = async function ConnectionFieldResolver( { a }: any ) {
			return findMany( a );
		};
		const descriptor :PropertyDescriptor = { configurable: true, enumerable: true, writable: true };
		args( target, newPropertyName, 0 );
		field( target, newPropertyName, descriptor );
	};
}

Expected Behavior
I expected that it create a function to resolve prueba field inside object type, but it throws a error

I can resolve the problem just adding a optional chaining in line 11 inside /dist/helpers/findType.js , just like

 metadataDesignType = reflectedType?.[parameterIndex];

Logs
at .../node_modules/type-graphql/dist/helpers/findType.js:11
metadataDesignType = reflectedType[parameterIndex];
^
TypeError: Cannot read property '0' of undefined
at .../node_modules/type-graphql/dist/helpers/findType.js:11:43)
at Object.getParamInfo (.../node_modules/type-graphql/dist/helpers/params.js:10:49)
at. .../node_modules/type-graphql/dist/decorators/Args.js:12:25

Environment (please complete the following information):

• OS: mac os
• Node 14.0
• Package version lastest
• TypeScript version 4.0.3

[techo207]

I've create a pull request to resolve it

#use optional chaining to get value inside reflectedType #725

[MichalLytek]

Reopening the issue as the proper fix is ready on #733