fix a swift compatibility issue

[shalehaha]

Description

Related Issue

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have signed the Adobe Open Source CLA.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[codecov]

Codecov Report

Merging #617 (a4badb0) into dev-v3.1.2 (953f4b6) will increase coverage by 0.07%.
The diff coverage is n/a.

@@              Coverage Diff               @@
##           dev-v3.1.2     #617      +/-   ##
==============================================
+ Coverage       85.30%   85.36%   +0.07%     
==============================================
  Files             104      104              
  Lines            4570     4570              
==============================================
+ Hits             3898     3901       +3     
+ Misses            672      669       -3