Solid 2: Nullish reactive JSX spreads crash rendering and halt updates #3297

Describe the bug

A lone reactive JSX spread crashes when its source is undefined or null. This affects valid optional-props patterns such as <input {...props()} />, where props() returns an object or an absent value.

The runtime throws TypeError: Cannot convert undefined or null to object. Without an enclosing error boundary, it reports REACTIVITY_HALTED and stops processing subsequent reactive updates.

Verified against source at a17dfec, whose package manifests identify the prerelease as 2.0.0-rc.6. This report describes that checkout, not a separate test of the published rc.6 bundles.

Minimal reproduction

Vitest/jsdom TSX test using the normal Solid JSX transform:

/** @jsxImportSource @solidjs/web */
import { expect, test } from "vitest";
import { createSignal, flush } from "solid-js";
import { render } from "@solidjs/web";

test.each([undefined, null])("clearing optional spread to %s", absent => {
  const host = document.createElement("div");
  const [props, setProps] = createSignal<
    { value: string } | undefined | null
  >({ value: "draft" });

  const dispose = render(() => <input {...props()} />, host);
  try {
    expect((host.firstElementChild as HTMLInputElement).value).toBe("draft");

    setProps(absent);
    flush(); // Throws before the assertion below.

    expect((host.firstElementChild as HTMLInputElement).value).toBe("");
  } finally {
    dispose();
  }
});

Starting with an undefined reactive spread also crashes the initial mount. TypeScript accepts the object-or-nullish accessor type above; this is not a definitely-null spread expression such as {...null}.

Expected behavior

Treat the absent source as empty props: retain the input, clear the previously supplied value, and continue processing application updates without throwing.

Actual behavior

Both nullish cases throw from hasOwnProperty in spread():

[REACTIVITY_HALTED] An uncaught error halted the reactive system.
No further updates will be processed.
TypeError: Cannot convert undefined or null to object
    at hasOwnProperty (<anonymous>)
    at packages/web/src/client.ts:724:21

Root cause

spread() at client.ts:720-730 resolves the accessor and calls hasOwn.call(source, "children") and hasOwn.call(source, "ref") without normalizing a nullish source.

Both compilers pass a lone reactive spread directly to this helper. In contrast, adding a static attribute, <input id="field" {...props()} />, selects the merged-props path and the same transitions pass.

Impact and verification

• Optional field configuration and conditional props can cause a mount failure or an application-wide reactive halt, rather than simply removing attributes.
• Reproduced with both the native and Babel JSX compilers against source-runtime aliases.
• Reproduced with development and production flags, and when removing the spread after successful hydration.
• Platform: macOS, Vitest 4.1.6, jsdom 25.0.1. These are source-runtime test results, not a browser compatibility claim.
• This differs from 2.0.0-beta.28: input props spread causes value to be `"undefined" when value is undefined #2957: the entire spread source is absent here, rather than an existing props object containing value: undefined.

Reported with OpenCode (GPT-6 Astra).