Treat None as an empty string in optional StringVar operations

FA
4h ago
+162-16

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Type of change

  • Bug fix (non-breaking change which fixes an issue)

Changes To Core Features:

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  • Have you written new tests for your core changes, as applicable?
  • Have you successfully ran tests with your changes locally?

Problem

A str | None state var holding None crashed the page for every string operation that compiles to a native string method:

class S(rx.State):
    m: str | None = None

rx.foreach(S.m.split(" "), rx.text)   # TypeError: Cannot read properties of null (reading 'split')

split with a separator, strip / lstrip / rstrip, lower, upper, title, capitalize, contains, startswith, endswith, replace and * all threw, and the whole page fell into the error boundary. length, indexing, slicing and split() already read None as "" through the code point helpers, so the behaviour depended on which operation was used.

Fix

This takes option 1 from #7873 (treat None as "" everywhere), which is the rule #7800 already set for optional lists and sets.

StringVar gets the same _or_empty() view ArrayVar has: when the var type allows None, the operation reads (x ?? ""), typed without None. A string that cannot be None compiles exactly as before, with no guard. The operations that go through a null-safe helper (pyStrLength, pyStrAt, pyStrSlice, pyStrChars) are left unguarded.

Not changed: + / f-string concatenation and the comparison operators, which do not throw on null.

Tests

  • tests/units/reflex_base/vars/test_sequence.py: the exact compiled JS of every guarded operation for an optional and a required string, the result types, and the helper-backed operations that stay unguarded.
  • tests/integration/tests_playwright/test_var_operations.py: the existing app renders the operations on an optional string holding None and on one holding a value. Without the fix the page does not render at all (TypeError: Cannot read properties of null in the browser).

Ran locally: tests/units (one unrelated browser-launch test in reflex_bench cannot start Chromium in my sandbox), the two string Playwright modules, ruff check, ruff format, and pyright on the changed files.

closes #7873

https://claude.ai/code/session_01LwJUCTCgM7D4Vj6H4dRWss

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