`Link` with `undefined` pathname should omit `href` attribute from `a` element

[lorumic]

I'm using React Router as a...

library

Reproduction

• Go to https://stackblitz.com/edit/github-bzaopgvp?file=app%2Froutes%2Fhome.tsx
• Inspect the two Links rendered in the Preview panel with the browser's developer tools: they both render an a element with href="/"

System Info

System:
    OS: Linux 6.11 Ubuntu 24.04.2 LTS 24.04.2 LTS (Noble Numbat)
    CPU: (22) x64 Intel(R) Core(TM) Ultra 7 165H
    Memory: 9.12 GB / 30.78 GB
    Container: Yes
    Shell: 5.2.21 - /usr/bin/bash
  Binaries:
    Node: 22.14.0 - ~/.nvm/versions/node/v22.14.0/bin/node
    Yarn: 1.22.22 - ~/.nvm/versions/node/v22.14.0/bin/yarn
    npm: 10.9.2 - ~/.nvm/versions/node/v22.14.0/bin/npm
    bun: 1.2.13 - ~/.nvm/versions/node/v22.14.0/bin/bun
  Browsers:
    Chrome: 138.0.7204.49
    Chromium: 137.0.7151.103
  npmPackages:
    vite: 6.3.5 => 6.3.5

Used Package Manager

yarn

Expected Behavior

• With <Link to={{ pathname: '' }}>, I expect to see rendered <a href="/">
• With <Link to={{ pathname: undefined }}>, I expect to see rendered <a>

Rationale: we use the Link component to be styled as a button, and this button needs to be disabled sometimes. When the button is disabled, we don't want to have any href attribute at all.

Actual Behavior

Empty string and undefined are treated in the same way by the Link component when passed as a pathname - they both render <a href="/">.