Fix small ARM conversion bug

[matthchr]

If there are no properties to actually perform conversion on, just return nil.

[matthchr]

Not sure if linting on the golden files would've caught this, but another situation where the golden files actually had a compiler error in it and I just didn't notice it initially.

[codecov-commenter]

Codecov Report

Merging #1524 (ba6f999) into master (662f514) will increase coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1524      +/-   ##
==========================================
+ Coverage   63.20%   63.23%   +0.03%     
==========================================
  Files         175      175              
  Lines       11573    11583      +10     
==========================================
+ Hits         7315     7325      +10     
  Misses       3601     3601              
  Partials      657      657              

Impacted Files	Coverage Δ
...armconversion/convert_from_arm_function_builder.go	89.09% <100.00%> (+0.34%)	⬆️
...ack/generator/pkg/astmodel/armconversion/shared.go	82.45% <100.00%> (+1.68%)	⬆️

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