SpringBoot REST API error: Column cannot be null (Kotlin)

@Entity
class User {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    var id: Int = 0
    var name: String = ""
    var email: String = ""
    var password: String = ""
        @JsonIgnore
        get
        set(value) {
            val passwordEncoder: PasswordEncoder = BCryptPasswordEncoder()
            field = passwordEncoder.encode(value)
        }
 
    @Enumerated(value = EnumType.STRING)
    var role: Role = Role.USER
 
    @OneToMany(cascade = [CascadeType.ALL])
    @JoinColumn(name = "userId")
    var tickets: MutableList<Ticket> = ArrayList()
 
    fun comparePassword(password: String): Boolean {
        return BCryptPasswordEncoder().matches(password, this.password)
    }
 
    fun deleteTicketByTicketId(ticketId: Int) {
        for (i in 0..(tickets.size - 1)) {
            if (tickets[i].id == ticketId) {
                tickets.removeAt(i)
            }
        }
    }
}

@Entity
class Ticket {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    val id: Int = 0
 
    @JsonIgnore
    var userId: Int = 0
    var fromCity: String = ""
    var toCity: String = ""
    var planeNumber: String = ""
    var place: Int = 0
    var date: String = ""
    var time: String = ""
}

@DeleteMapping("{ticketId}")
    fun deleteTicket(@PathVariable ticketId: Int, @CookieValue("jwt") jwt: String?): ResponseEntity<Any> {
        try {
            if (jwt == null) {
                return ResponseEntity.status(401).body("unauthenticated")
            }
            //get user
            val userFromDB = getUserFromJWT(jwt)
            println("1")
            //remove ticket from user.List<Ticket>
            userFromDB.deleteTicketByTicketId(ticketId)
            println("2")
            //remove ticket from DB
            ticketService.deleteById(ticketId)
            println("3")
            return ResponseEntity.ok("success")
        } catch (e: Exception) {
            println("4")
            return ResponseEntity.status(401).body("unauthenticated")
        }
    }

fun deleteById(id: Int){
        val ticket = ticketRepository.findById(id).get()
        ticketRepository.delete(ticket)
    }