Add non-null constraint for optional fields in GraphQL input types

[kobinarth-panchalingam]

When defining input types in GraphQL, using the non-null constraint on a field makes it required, which poses a challenge for optional fields that should not accept null values. We need a way to define optional fields that cannot be null if provided. For example, an email field should either be omitted or provided with a non-null value, but currently, the non-null constraint forces it to always be required.