我试图将数据保存到实时数据库的firebase。但我得到这个错误

com.google.firebase.database.DatabaseException: No properties to serialize found on class java.lang.StringBuilder
at com.google.firebase.database.core.utilities.encoding.CustomClassMapper$BeanMapper.<init>(CustomClassMapper.java:548)
at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.loadOrCreateBeanMapperForClass(CustomClassMapper.java:330)
at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.serialize(CustomClassMapper.java:167)
at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.serialize(CustomClassMapper.java:142)
at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertToPlainJavaTypes(CustomClassMapper.java:61)
at com.google.firebase.database.DatabaseReference.setValueInternal(DatabaseReference.java:282)
at com.google.firebase.database.DatabaseReference.setValue(DatabaseReference.java:159)

我以前的项目，我使用相同的代码，但现在我得到这个错误。
下面是我用来保存数据的函数代码

private fun saveDetails() {

    val userDataRef: DatabaseReference =
        FirebaseDatabase.getInstance().reference.child("UsersData").child(currentUserId)

    val userMap = HashMap<String, Any>()
    userMap["name"] = name
    userMap["email"] = email
    userMap["imageUrl"] = profileImageUrl
    userMap["phoneNumber"] = number

        userDataRef.setValue(userMap).addOnCompleteListener { task ->
            if (task.isSuccessful) {
                Toast.makeText(
                    baseContext,
                    "$name has successfully registered with email id $email.",
                    Toast.LENGTH_SHORT
                ).show()
                startActivity(Intent(this, MainActivity::class.java))
            } else {
                Toast.makeText(baseContext, task.result.toString(), Toast.LENGTH_SHORT).show()
                Log.e("Task  Unsuccessful", task.result.toString())
            }
        }
    }