~savoy/holo#3: 
better handling of empty DataFrames

Unlike pandas, polars empty DataFrames do not hold column data. holo currently held the assumption that it did. As such, attempting to run queries that pull zero data from SQL will spit out errors similar to below:

Error originated just after this operation:
DF []; PROJECT */0 COLUMNS; SELECTION: "None"

Any creation of a DataFrame needs to be checked with is_empty() so that only non-empty DataFrames are concatenated or attempted to be modified etc., and if only one DataFrame is being modified/outputted (i.e. Data.to_pager()), a graceful output message about no data should be printed.

Status
REPORTED
Submitter
~savoy
Assigned to
Submitted
1 year, 8 days ago
Updated
1 year, 8 days ago
Labels
bug