Warn for malformed urls

[felixcremer]

I tried to follow along a python STAC example and tried to use a malformed url this doesn't work because of the unnecessary collections at the end.

Would there be a way to check for these malformed urls so that users would be notified, that this doesn't work?

(STAC) julia> url = "https://stac.core.eopf.eodc.eu/collections"
"https://stac.core.eopf.eodc.eu/collections"

(STAC) julia> cat = STAC.Catalog(url)
nothing

[Alexander-Barth]

Thanks for the issue report! With the current commit, we now have the following error message:

julia> STAC.Catalog(url)
ERROR: ArgumentError: The mandatory STAC id element is missing in https://stac.core.eopf.eodc.eu/collections

[Alexander-Barth]

I considered to use mandatory type field (which should have the value Catalog), but it is not present in some example catalogs that I use for testing (https://raw.githubusercontent.com/sat-utils/sat-stac/master/test/catalog/catalog.json).