Fixes an error when no config file present (assume default config) + tests

[athril]

• fixes SparcClient without config file fails #40
• updates to client.py and test_client.py when no config/incorrect config provided

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (e39a579) to head (c71a2c0).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #41   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            9         9           
  Lines          446       450    +4     
=========================================
+ Hits           446       450    +4     

Flag	Coverage Δ
unittests	100.00% <100.00%> (ø)

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[hsorby]

Looks good, just one very minor change.