Null check operator used on a null value error

[jihuncha]

Hello, I'm using UML diagram generation through GitHub Actions, and I've encountered the following error after modifying an object recently:

Null check operator used on a null value #0 ElementAnnotationExtensions.targetKinds (package:analyzer/src/dart/element/extensions.dart:42:51) #1 BestPracticesVerifier.visitAnnotation (package:analyzer/src/error/best_practices_verifier.dart:299:25) #2 AnnotationImpl.accept (package:analyzer/src/dart/ast/ast.dart:298:50) #3 NodeListImpl.accept (package:analyzer/src/dart/ast/ast.dart:7758:20) #4 AnnotatedNodeImpl.visitChildren (package:analyzer/src/dart/ast/ast.dart:145:17) #5 ClassDeclarationImpl.visitChildren (package:analyzer/src/dart/ast/ast.dart:1510:11) #6 RecursiveAstVisitor.visitClassDeclaration (package:analyzer/dart/ast/visitor.dart:746:10) #7 BestPracticesVerifier.visitClassDeclaration (package:analyzer/src/error/best_practices_verifier.dart:371:13) #8 ClassDeclarationImpl.accept (package:analyzer/src/dart/ast/ast.dart:1487:50) #9 NodeListImpl.accept (package:analyzer/src/dart/ast/ast.dart:7758:20) #10 CompilationUnitImpl.visitChildren (package:analyzer/src/dart/ast/ast.dart:2095:21) #11 RecursiveAstVisitor.visitCompilationUnit (package:analyzer/dart/ast/visitor.dart:770:10) #12 CompilationUnitImpl.accept (package:analyzer/src/dart/ast/ast.dart:2088:50) #13 LibraryAnalyzer._computeHints (package:analyzer/src/dart/analysis/library_analyzer.dart:358:10) #14 LibraryAnalyzer.analyze.<anonymous closure> (package:analyzer/src/dart/analysis/library_analyzer.dart:166:9) #15 LinkedHashMapMixin.forEach (dart:collection-patch/compacthash.dart:633:13) #16 LibraryAnalyzer.analyze (package:analyzer/src/dart/analysis/library_analyzer.dart:165:13) #17 AnalysisDriver._computeAnalysisResult.<anonymous closure> (package:analyzer/src/dart/analysis/driver.dart:1455:63) #18 PerformanceLog.run (package:analyzer/src/dart/analysis/performance_logger.dart:32:15) #19 AnalysisDriver._computeAnalysisResult (package:analyzer/src/dart/analysis/driver.dart:1431:20) #20 AnalysisDriver.performWork (package:analyzer/src/dart/analysis/driver.dart:1055:22) #21 AnalysisDriverScheduler._run (package:analyzer/src/dart/analysis/driver.dart:2140:24) <asynchronous suspension> #0 AnalysisDriver._computeAnalysisResult.<anonymous closure> (package:analyzer/src/dart/analysis/driver.dart:1484:9) #1 PerformanceLog.run (package:analyzer/src/dart/analysis/performance_logger.dart:32:15) #2 AnalysisDriver._computeAnalysisResult (package:analyzer/src/dart/analysis/driver.dart:1431:20) #3 AnalysisDriver.performWork (package:analyzer/src/dart/analysis/driver.dart:1055:22) #4 AnalysisDriverScheduler._run (package:analyzer/src/dart/analysis/driver.dart:2140:24)

I'm using @JsonSerializable() in my model. Could this be causing the issue? I couldn't find any similar issues, so I'm creating this to inquire about the problem. Thank you for your assistance.