How to solve the internal server error in response body in swagger?

from fastapi import FastAPI, HTTPException, Depends
from pydantic import BaseModel, Field
import models
from database import engine, SessionLocal
from sqlalchemy.orm import Session

app = FastAPI()

models.Base.metadata.create_all(bind=engine)


def get_db():
    try:
        db = SessionLocal()
        yield db
    finally:
        db.close()


class Employee(BaseModel):
    first_name: str = Field(min_length=1)
    last_name: str = Field(min_length=1, max_length=100)
    city: str = Field(min_length=1, max_length=100)
    experience: int = Field(gt=-1, lt=101)
    ctc: int = Field()
    age: int = Field(gt=-1, lt=101)
    contact: str = Field(min_length=1, max_length=100)

EMPLOYEE = []

@app.get('/')
async def root():
    return {'message': 'Hello World!'}

@app.get("/read_api")
def read_api(db: Session = Depends(get_db)):
    return db.query(models.Employees).all()


@app.post("/")
def create_book(employee: Employee, db: Session = Depends(get_db)):

    employee_model = models.Employees()
    employee_model.first_name = employee.first_name
    employee_model.last_name = employee.last_name
    employee_model.city = employee.city
    employee_model.experience = employee.experience
    employee_model.ctc = employee.ctc
    employee_model.age = employee.age
    employee_model.contact = employee.contact

    db.add(employee_model)
    db.commit()

    return employee


@app.put("/{emp_id}")
def update_employee(emp_id: int, employee: Employee, db: Session = Depends(get_db)):

    employee_model = db.query(models.Employees).filter(models.Employees.id == emp_id).first()

    if employee_model is None:
        raise HTTPException(
            status_code=404,
            detail=f"ID {emp_id} : Does not exist"
        )

    employee_model.first_name = employee.first_name
    employee_model.last_name = employee.last_name
    employee_model.city = employee.city
    employee_model.experience = employee.experience
    employee_model.ctc = employee.ctc
    employee_model.age = employee.age
    employee_model.contact = employee.contact

    db.add(employee_model)
    db.commit()

    return employee


@app.delete("/{emp_id}")
def delete_employee(emp_id: int, db: Session = Depends(get_db)):

    employee_model = db.query(models.Employees).filter(models.Employees.id == emp_id).first()

    if employee_model is None:
        raise HTTPException(
            status_code=404,
            detail=f"ID {emp_id} : Does not exist"
        )

    db.query(models.Employees).filter(models.Employees.id == emp_id).delete()

    db.commit()