Fix serialization error in curl api

[freddyaboulton]

Description

Closes #9184

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Fix serialization error in curl api

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[abidlabs]

LGTM nice fix @freddyaboulton! I did some testing to make sure that this didn't break any demos that don't have a dataclass, and added a test for it in our test suite

[freddyaboulton]

Thanks for the test @abidlabs !