Remove empty namespace from builder

[superstar54]

Fix #1069

In principle the plugin's workchain should validate a input namespace is empty or not, but not all developers are doing this, see the xas issue: aiidateam/aiida-quantumespresso#1057

Here we remove the empty namespace for safety.

Edit: This change will affect all plugins, and we assume all empty namespaces are not used, which is by default when submitting a builder in the aiida-core.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 67.91%. Comparing base (75a792d) to head (a925b3d).
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1073      +/-   ##
==========================================
+ Coverage   67.90%   67.91%   +0.01%     
==========================================
  Files         113      113              
  Lines        6689     6689              
==========================================
+ Hits         4542     4543       +1     
+ Misses       2147     2146       -1     

Flag	Coverage Δ
python-3.11	67.91% <100.00%> (+0.01%)	⬆️
python-3.9	67.93% <100.00%> (+0.01%)	⬆️

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[edan-bainglass]

Sure. LGTM!