Create vendor without user create a null user vendor.

[shovan777]

What I'm trying to achieve

I accidentally created a vendor without user and it allowed me to do so.

Steps to reproduce the problem

1. Create a vendor with vendor create mutation.
2. Leave the user argument in the mutation.
3. Vendor is created with null user

What I expected to happen

I expected that an error would occur and I should not be able to create a vendor before it is a user object.

But instead what happened is I could create the vendor with null user.

System information

Saleor version:

• dev (current master)
• 3.0
• 2.11
• 2.10

Operating system:

• Windows
• Linux
• MacOS
• Other

[mehmetaydogduu]

I think this is simple to solve. We have only marketplace branch here, I uploaded your code to this repository, can you push latest changes if exists?