Cannot use a relationship field named 'items'

[Shavinder]

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Example Code

from typing import Optional
from sqlmodel import SQLModel, Field, Relationship   

class Invoice(SQLModel, table=True):
    __tablename__ = "invoices"
    customer: str
    id: Optional[int] = Field(default=None, primary_key=True)
    # relationship
    items: Optional[list["Item"]] = Relationship(back_populates="invoice")
    # itemsx: Optional[list["Item"]] = Relationship(back_populates="invoice")

class Item(SQLModel, table=True):
    __tablename__ = "items"
    name: str
    id: Optional[int] = Field(default=None, primary_key=True)
    school_id: int = Field(default=None, foreign_key="invoices.id")
    # relationship
    invoice: "Invoice" = Relationship(back_populates="items")
    # invoice: "Invoice" = Relationship(back_populates="itemsx")

Description

On running this code:
inv=Invoice.model_validate({'customer':'ABC'})

I get this error:
TypeError: Incompatible collection type: builtin_function_or_method is not list-like

Operating System

Windows

Operating System Details

No response

SQLModel Version

0.0.19

Python Version

3.12.0

Additional Context

No response