[REF-3192] rx.foreach over computed var list fails

[SlonSky]

Describe the bug

When I try to render list that is produced by computed state var, I encounter Server Error "TypeError: Cannot read properties of undefined (reading 'map')"

To Reproduce

• Define computed var that returns a list in the State.
• Use that state var in rx.foreach

import reflex as rx

class ExampleState(rx.State):

    @rx.var
    def items(self) -> list[str]:
        return list(str(i) for i in range(10))

def index():
    return rx.vstack(
        rx.foreach(
            ExampleState.items,
            lambda item: rx.text(item)
        )
    )

app = rx.App()
app.add_page(index)

Expected behavior

the rx.foreach will render 10 text elements

Screenshots

Specifics (please complete the following information):

• Python Version: 3.12.2
• Reflex Version: 0.5.5

Additional context

Very similar to the old issue https://github.com/reflex-dev/reflex/issues/1886 and the same hack works:

import reflex as rx

class ExampleState(rx.State):

    @rx.var
    def items(self) -> list[str]:
        return list(str(i) for i in range(10))

def index():
    return rx.vstack(
        rx.cond(
            ExampleState.items,
            rx.foreach(
                ExampleState.items,
                lambda item: rx.text(item)   
            )    
        )   
    )

app = rx.App()
app.add_page(index)

Also, everything works when the state var isn't computed (however it forces us to have some event handler that constatly updates the var):

import reflex as rx

class ExampleState(rx.State):
    items: list[str] = ['a', 'b', 'c']

def index():
    return rx.vstack(
        rx.foreach(
            ExampleState.items,
            lambda item: rx.text(item)   
        )    
    )

app = rx.App()
app.add_page(index)

_REF-3192

[Lendemor]

Tried to reproduce it on latest main, but your code snippet is working for me.

[picklelo]

@SlonSky I believe this is because somewhere your ExampleState.items is being set to None rather than an empty list. Then in Javascript, it's unable to call the map function leading to this error.