Pydantic input model for partial updates

I am using Pydantic to validate data inputs in a server. Pydantic models:

• User: for common fields
• UserIn: user input data to create new account
• UserInDB: to hash password and include extra fields like created_at
• UserOut: to output created/updated user data

Now how can I utilize the model UserIn for user account partial updates? so that None fields are excluded. Or do I have to rewrite it again and make every field optional?

class User(BaseModel):

    name_first :          str = Field(...)
    name_last :           Optional[str] = None
    mobile :              int = Field(..., description="It has to be 8 digits and starts with either 9 or 7", example="99009900")
    
    email :               Optional[EmailStr] = None
    
    gender:               Literal['m', 'f'] = Field(..., example="m")
    birth_date:           datetime.date
    preferred_language :  Literal['ar', 'en'] = Field(..., example="ar")
    newsletter :          bool = Field(...)


    @validator('mobile')
    def number_has_to_start_with_9_or_7(cls, v):
        if str(v)[:1] !="9" and str(v)[:1] !="7":
            raise ValueError('Mobile number must start with 9 or 7')
        if len(str(v)) !=8:
            raise ValueError('Mobile number must be 8 digits')
        return v


class UserIn(User):
    password: str = Field(...)

class UserInDB(UserIn):
    mobile_otp:           int = Field(...)
    bitrole:              int = Field(...)
    created_at:           datetime.datetime
    updated_at:           datetime.datetime

class UserOut(User):
    id:                   int
    mobile_otp:           int
    bitrole:              int
    mobile_confirmed :    bool
    email_confirmed :     bool
    disabled :            bool
    created_at:           datetime.datetime
    updated_at:           datetime.datetime

    class Config:
        orm_mode = True