test(rest): cover SSE completion and parsing error outcomes - #1209

[RequireExplicitNullMarking] [RequireExplicitNullMarking] Top-level classes must either be directly annotated with @NullMarked/@NullUnmarked, be in a package that is explicitly @NullMarked/@NullUnmarked, or be in a module that is explicitly @NullMarked.

[RequireExplicitNullMarking] [RequireExplicitNullMarking] Top-level classes must either be directly annotated with @NullMarked/@NullUnmarked, be in a package that is explicitly @NullMarked/@NullUnmarked, or be in a module that is explicitly @NullMarked.

[RequireExplicitNullMarking] [RequireExplicitNullMarking] Top-level classes must either be directly annotated with @NullMarked/@NullUnmarked, be in a package that is explicitly @NullMarked/@NullUnmarked, or be in a module that is explicitly @NullMarked.

[RequireExplicitNullMarking] [RequireExplicitNullMarking] Top-level classes must either be directly annotated with @NullMarked/@NullUnmarked, be in a package that is explicitly @NullMarked/@NullUnmarked, or be in a module that is explicitly @NullMarked.

[RequireExplicitNullMarking] [RequireExplicitNullMarking] Top-level classes must either be directly annotated with @NullMarked/@NullUnmarked, be in a package that is explicitly @NullMarked/@NullUnmarked, or be in a module that is explicitly @NullMarked.

[RequireExplicitNullMarking] [RequireExplicitNullMarking] Top-level classes must either be directly annotated with @NullMarked/@NullUnmarked, be in a package that is explicitly @NullMarked/@NullUnmarked, or be in a module that is explicitly @NullMarked.

[RequireExplicitNullMarking] [RequireExplicitNullMarking] Top-level classes must either be directly annotated with @NullMarked/@NullUnmarked, be in a package that is explicitly @NullMarked/@NullUnmarked, or be in a module that is explicitly @NullMarked.

[RequireExplicitNullMarking] [RequireExplicitNullMarking] Top-level classes must either be directly annotated with @NullMarked/@NullUnmarked, be in a package that is explicitly @NullMarked/@NullUnmarked, or be in a module that is explicitly @NullMarked.

[RequireExplicitNullMarking] [RequireExplicitNullMarking] Top-level classes must either be directly annotated with @NullMarked/@NullUnmarked, be in a package that is explicitly @NullMarked/@NullUnmarked, or be in a module that is explicitly @NullMarked.

[RequireExplicitNullMarking] [RequireExplicitNullMarking] Top-level classes must either be directly annotated with @NullMarked/@NullUnmarked, be in a package that is explicitly @NullMarked/@NullUnmarked, or be in a module that is explicitly @NullMarked.