Mutations are not working with Apollo Client : passing variables

I am using an Angular Client with angular-apollo https://apollo-angular.com/docs/data/mutations and Mutations are throwing an error even though the variables are passed.

This is with Cosmos DB as storage.

**Client Code :**
```
const post_SaveHero = gql`
mutation ($id : String!, $publisher : String!, $superhero :String!, $characters:String!){
addHero(id : $id , publisher : $publisher , superhero : $superhero , characters: $characters )
{
superhero
}
}`;
```
Invoking it as,

```
updateHero(hero: Hero){
console.log("$$$HERO",hero.id);
console.log("$$$HERO OBJECT",JSON.stringify(hero));
return this.apollo.mutate({
mutation: post_SaveHero,
variables: {
id: hero.superhero,
publisher: hero.publisher,
superhero: hero.superhero,
characters: hero.characters
}
}
);
}

```
and the error thrown as,