Refactor: Updating to Dart 2.18#28

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nathanael-all-win-software wants to merge 3 commits intoBackendless:developfrom

nathanael-all-win-software:dart-warnings

Commits on Jun 28, 2022

Merge pull request #25 from Backendless/develop
holailusoria
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Commits on Jul 1, 2022

Merge pull request #26 from Backendless/develop
holailusoria
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Commits on Sep 18, 2022

Removing dart 2.18 warnings
nathanael-all-win-software
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