Feature Request/ Bug report: Fields are not marked as nullable in json schema

[martinostvik]

If you choose to set json_schema_extra={"nullable": False}) etc on the original model, the resulting model will not be marked as nullable in the json schema for the model.

Example:

from pydantic import BaseModel, Field
from pydantic_partial import create_partial_model

class A(BaseModel):
    name: str = Field(default="Bob", json_schema_extra={"required": True})

class B(BaseModel):
    name: str = Field(default="Bob", json_schema_extra={"nullable": False})

class C(BaseModel):
    name: str = Field(default="Bob")
    
PartialA = create_partial_model(A)
PartialB = create_partial_model(B)
PartialC = create_partial_model(C)

print(PartialA.model_json_schema())
print(PartialB.model_json_schema())
print(PartialC.model_json_schema())

Partial A:

{
   "properties":{
      "name":{
         "default":"Bob",
         "required":true,  <---- required and not nullable
         "title":"Name",
         "type":"string"
      }
   },
   "title":"A",
   "type":"object"
}

PartialB:

{
   "properties":{
      "name":{
         "default":"Bob",
         "nullable":false, <--- Not nullable
         "title":"Name",
         "type":"string"
      }
   },
   "title":"B",
   "type":"object"
}

PartialC: (Has a default value, and no "required" or "nullable" values. Means it is nullable)

{
   "properties":{
      "name":{
         "default":"Bob",
         "title":"Name",
         "type":"string"
      }
   },
   "title":"C",
   "type":"object"
}

I created a PR here to address this issue