graphene

Ensure that Graphene's scalar types are referenced with the correct capitalization (e.g., `graphene.String` instead of `graphene.string`).

```python
import graphene

class MyType(graphene.ObjectType):
    my_field = graphene.String()
```

Ensure that `graphql_jwt.middleware.JSONWebTokenMiddleware` is correctly added to both Django's `MIDDLEWARE` list and Graphene's `GRAPHENE` setting under `'MIDDLEWARES'` (note the plural 'S').

```python
# settings.py
MIDDLEWARE = [
    # ... other Django middleware
    'django.contrib.auth.middleware.AuthenticationMiddleware',
    'graphql_jwt.middleware.JSONWebTokenMiddleware',
    # ...
]

GRAPHENE = {
    'SCHEMA': 'your_project.schema.schema',
    'MIDDLEWARES': [
        'graphql_jwt.middleware.JSONWebTokenMiddleware',
    ],
}
```

Debug the resolver chain to identify where `None` is being returned instead of an object. Ensure that parent resolvers return valid objects (or dictionaries) and that `info.context` is properly populated if you are relying on it.

```python
# Example of a resolver returning None incorrectly
# def resolve_my_field(root, info):
#     user = User.objects.filter(id=root.user_id).first() # if user is not found, it's None
#     return user.name # This would raise the error if user is None

# Corrected resolver
def resolve_my_field(root, info):
    user = User.objects.filter(id=root.user_id).first()
    if user:
        return user.name
    return None # Or raise a specific error/return a default value
```

Upgrade Graphene and its dependencies to compatible versions. If you are on an older Graphene version, consider upgrading to Graphene 3.x, which usually has updated dependency ranges. Alternatively, you might need to pin `graphql-core` to a specific version known to be compatible with your Graphene installation.

```bash
pip install --upgrade graphene graphql-core
# If still problematic, try pinning graphql-core (e.g., for older Graphene versions)
# pip install graphene==2.1.8 graphql-core==2.3.2
```

When defining GraphQL types that represent Django models, ensure you import `DjangoObjectType` from `graphene_django.types` and inherit from it, especially in mutations where input fields are derived from the model.

```python
# Wrong:
# from graphene import ObjectType
# class MyModelType(ObjectType):
#     class Meta:
#         model = MyModel

# Correct:
from graphene_django.types import DjangoObjectType

class MyModelType(DjangoObjectType):
    class Meta:
        model = MyModel
```