only validate FI IdentificationCode when present or required

[atonks2]

What does this pull request do?
This PR fixes a bug where the value of FinancialInstitution.IdentificationCode was being validated when it was actually supposed to be empty.

What Wire specification are you referencing?
Fedwire Application Interface Manual (FAIM) Version 3.0.4

[codecov-commenter]

Codecov Report

Merging #365 (0952e78) into master (ebf16d9) will increase coverage by 0.04%.
The diff coverage is 100.00%.

❗ Current head 0952e78 differs from pull request most recent head 3421101. Consider uploading reports for the commit 3421101 to get more accurate results

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #365      +/-   ##
==========================================
+ Coverage   74.82%   74.86%   +0.04%     
==========================================
  Files          73       73              
  Lines        8684     8682       -2     
==========================================
+ Hits         6498     6500       +2     
+ Misses       1619     1615       -4     
  Partials      567      567              

[wadearnold]

Thank you!