Svelte 5: Error: x is undefined

[98mux]

Describe the bug

if you access a prop with no default value in a on:click then you get the error "x is undefined" (in non-rune mode)
Also found when trying to migrate from 4->5

Reproduction

https://svelte-5-preview.vercel.app/#H4sIAAAAAAAAA42O0QrCMAxFf6XkZRuM9X1uA_0N64N2rRS3tnSZKKP_bjpxIL5IIOm93KRnAW0GNUF9XMCeRwU17L2HEvDpk5juakBFenJzkMlpJhmMx05YgWb0LiA7zFemgxtZVnF6V--lTNiGb-FmDbUCMMxKAO_o5uh6o43qoU5mLDcEyv6LoB4rwqCQ6d3XjyQuM6KzKeasHIy8tUtesLZjS_KIX7NcFx9Ftc6YRqTO6cov5im-ANRMnfY1AQAA

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System Info

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Severity

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