[BUG] _fix_anno fails to gracefully handle type conversion for non-strings

[wafflesatdawn]

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Describe the bug

The problem is with your Optional[float] type annotation for the price parameter . When FastHTML encounters an empty string from your form submission, it attempts to convert it to a float, which fails and triggers the 404 error core.py:204-205 .

Here's what's happening in the _fix_anno function when processing your Optional[float] parameter core.py:83-92 :

FastHTML extracts the first non-None type from the union (Optional[float] becomes float) core.py:86-87
It tries to convert the empty string "" to float(""), which raises a ValueError
This ValueError is caught and converted to a 404 error core.py:204-205

Minimal Reproducible Example
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# Your code here

Expected behavior
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Environment Information
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• fastlite version:
• fastcore version:
• fasthtml version:

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• I have read the FAQ (https://docs.fastht.ml/explains/faq.html)
• I have provided a minimal reproducible example
• I have included the versions of fastlite, fastcore, and fasthtml
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