Non consistent reactivity with style:value / undefined and empty string

[dm-de]

Describe the bug

style:value works different, if you set empty string or undefined.
Once a style-value is set, it can no more removed with undefined!
But empty string can remove value.
see example in reproduction

<div style:font-family={undefined}>div 1</div>
<div style:background={undefined}>div 2</div>
<div style:font-family={''}>div 3</div>
<div style:background={''}>div 4</div>

note that style:font-family generate this wrong code:
<div style="font-family: undefined;">div 1</div>
here are possible other style-values that can generate wrong code (?)

Reproduction

https://svelte.dev/repl/21ee1c2341fe44e9ae2b9994fcd99253?version=3.58.0

Resize html result.
Left side of "content" should change.
But once it moves, it never returns back.

at line:
style:left={left_ ? left_ + 'px' : undefined}
replace undefined with ''
now it works like expected

Logs

No response

System Info

svelte 3.58.0
vite

Severity

annoyance

[Prinzhorn]

#7580
#7446

[Conduitry]

This has been fixed in 3.59.0 - https://svelte.dev/repl/21ee1c2341fe44e9ae2b9994fcd99253?version=3.59.0