Getting error "Nullability Mismatch on variable $fulfillment....." when invoking a graphQL mutation

[Ashfaq_]

Nullability Mismatch on variable $fulfillment and argument fulfillment (FulfillmentV2Input/FulfillmentV2Input!)

After failing to call the fulfillment API using Rest, I went ahead with integrating the same thing using GraphQL but I am unable to understand why I am encountering this error.

Documentation for reference: https://shopify.dev/api/admin-graphql/2022-01/mutations/fulfillmentCreateV2