Changed validation in ChatLinkDto.java from @NotBlank to @NotNull

[KizerovDmitriy]

GreenCityUBS PR (dev)

Summary Of Changes 🔥

• changed validation in ChatLinkDto.java.
• added tests.

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• Code is up-to-date with the dev branch.
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• There are new or updated unit tests validating the change.
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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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