Fix Concatenation Error

[lawrence-mbf]

Motivation

Fixes #544

How to test the behavior?

See #544

Checklist

• [x] Have you ensured the PR description clearly describes the problem and solutions?
• [x] Have you checked to ensure that there aren't other open or previously closed Pull Requests for the same change?
• [x] If this PR fixes an issue, is the first line of the PR description fix #XX where XX is the issue number?

[codecov[bot]]

Codecov Report

Merging #545 (ce9c997) into master (a80f0aa) will increase coverage by 0.03%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #545      +/-   ##
==========================================
+ Coverage   87.78%   87.82%   +0.03%     
==========================================
  Files         132      132              
  Lines        5626     5627       +1     
==========================================
+ Hits         4939     4942       +3     
+ Misses        687      685       -2     

Files Changed	Coverage Δ
NwbFile.m	82.97% <100.00%> (+0.12%)	:arrow_up:

... and 2 files with indirect coverage changes

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