TCGA updates

[taraeicher]

Added additional catch for zero-variance values during t-test.

[codecov]

Codecov Report

❌ Patch coverage is 90.90909% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 71.16%. Comparing base (a412264) to head (90bffe2).
⚠️ Report is 3 commits behind head on devel.

Files with missing lines	Patch %	Lines
R/SEAHORSE.R	90.90%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##            devel     #425      +/-   ##
==========================================
+ Coverage   71.14%   71.16%   +0.01%     
==========================================
  Files          22       22              
  Lines        4474     4480       +6     
==========================================
+ Hits         3183     3188       +5     
- Misses       1291     1292       +1     

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