This also works:
nulldata 26 # But you must know the size beforehand
series test = get_series_BSL("LAUCN040010000000005")
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The result is not what you wanted. It is not a time series. And the series test would have "value" as description".
I also think that passing a file name and let the user then process it, to be a good choice.
(At first I considered to use a command mktmp to create a temporary filename, but Windows might not have it)
If the function is easily adaptable for different Online Databases, just having the url and the fields logic, users could contribute with more examples.