fix(@aws-amplify/ui-components): handle non-username alias cases

[wlee221]

Issue #, if available: fixes #7636

Description of changes: Checks for empty string and undefined before doing any string operation.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

Merging #7663 (cc36343) into main (1602377) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #7663   +/-   ##
=======================================
  Coverage   74.10%   74.10%           
=======================================
  Files         214      214           
  Lines       13405    13405           
  Branches     2626     2626           
=======================================
  Hits         9934     9934           
  Misses       3272     3272           
  Partials      199      199           

Impacted Files	Coverage Δ
packages/core/src/Platform/version.ts	100.00% <100.00%> (ø)

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[sammartinez]

LGTM 🌮

[github-actions]

This pull request has been automatically locked since there hasn't been any recent activity after it was closed. Please open a new issue for related bugs.

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