Fix for the case of add tag or add nickname args are nill

[m-t-a-n-a-k-a]

close #265

I'm not sure if this is the best fix in terms of where throwing exceptions. Please tell me your opinion🙏 Thank you.

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Hi there! Thanks so much for submitting a pull request!

Let's just make sure together that all of these boxes are checked before we merge this change:

• [x] The code in these changes works correctly.
• [x] Code has tests as appropriate.
• [x] Code has been reviewed by @JacobEvelyn.
• [x] All tests pass on Travis CI.
• [x] Code coverage remains high.
• [x] Rubocop reports no issues on Travis CI.
• [x] The README.md file is updated as appropriate.

Don't worry—this list will get checked off in no time!

[codecov[bot]]

Codecov Report

Merging #266 into main will increase coverage by 0.00%. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #266   +/-   ##
=======================================
  Coverage   98.41%   98.41%           
=======================================
  Files          24       24           
  Lines         755      757    +2     
=======================================
+ Hits          743      745    +2     
  Misses         12       12           

Impacted Files	Coverage Δ
lib/friends/commands/add.rb	100.00% <100.00%> (ø)
lib/friends/introvert.rb	98.70% <100.00%> (+<0.01%)	:arrow_up:

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[JacobEvelyn]

Thank you, @m-t-a-n-a-k-a! This change is now released in version 0.53!