Only wrap a type in an optional if it is not nil

[turbolent]

Fix by @SupunS 👏

Same as #936, against master

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• Targeted PR against master
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work
• Code follows the standards mentioned here
• Updated relevant documentation
• Re-reviewed Files changed in the Github PR explorer
• Added appropriate labels

[codecov-commenter]

Codecov Report

Merging #937 (9505d86) into master (2d95036) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #937   +/-   ##
=======================================
  Coverage   74.19%   74.19%           
=======================================
  Files         267      267           
  Lines       32993    32994    +1     
=======================================
+ Hits        24479    24480    +1     
  Misses       7386     7386           
  Partials     1128     1128           

Flag	Coverage Δ
unittests	74.19% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
runtime/sema/check_force_expression.go	90.90% <100.00%> (-0.76%)	⬇️
runtime/sema/check_invocation_expression.go	98.69% <100.00%> (ø)
runtime/sema/check_reference_expression.go	100.00% <100.00%> (ø)
runtime/sema/checker.go	89.94% <100.00%> (+0.03%)	⬆️

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[SupunS]

Thank you for the PR!