Panic: runtime error invalid memory address or nil pointer dereference when using generic types

[okliuxing]

Describe the bug
I encountered a runtime error while running swag init with generic types in Go. Here are the details:

Error Log:

PS C:\Project> swag init --v3.1  -g handler/handler.go --parseDependency --parseInternal
Swag version:  v2.0.0
...
2025/03/25 15:38:40 Generating UserInfo
panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xc0000005 code=0x0 addr=0x18 pc=0x11d6eaa]

goroutine 1 [running]:
github.com/swaggo/swag/v2.fillDefinitionDescriptionV3(0xc0000a2000, 0xc019702908, 0x154af50?, 0xc019635740)
        C:/Users/null/go/pkg/mod/github.com/swaggo/swag/v2@v2.0.0-rc4/parserv3.go:768 +0x2a
github.com/swaggo/swag/v2.(*Parser).ParseDefinitionV3(0xc0000a2000, 0xc019635740)
        C:/Users/null/go/pkg/mod/github.com/swaggo/swag/v2@v2.0.0-rc4/parserv3.go:725 +0x43a
github.com/swaggo/swag/v2.(*Parser).getTypeSchemaV3(0xc0000a2000, {0xc0189ddc40, 0x1d}, 0xc000c1c640, 0x1)
        C:/Users/null/go/pkg/mod/github.com/swaggo/swag/v2@v2.0.0-rc4/parserv3.go:669 +0xa06
github.com/swaggo/swag/v2.(*Parser).parseStructFieldV3(0xc0000a2000, 0xc000c1c640, 0xc0196b4180)
        C:/Users/null/go/pkg/mod/github.com/swaggo/swag/v2@v2.0.0-rc4/parserv3.go:973 +0x391
github.com/swaggo/swag/v2.(*Parser).parseStructV3(0xc0000a2000, 0xc000c1c640, 0xc01bdf43c0)
        C:/Users/null/go/pkg/mod/github.com/swaggo/swag/v2@v2.0.0-rc4/parserv3.go:885 +0xca
github.com/swaggo/swag/v2.(*Parser).parseTypeExprV3(0xc0000a2000, 0x145d195?, {0x154b010?, 0xc01b5507e0?}, 0xe0?)
        C:/Users/null/go/pkg/mod/github.com/swaggo/swag/v2@v2.0.0-rc4/parserv3.go:808 +0x447
github.com/swaggo/swag/v2.(*Parser).ParseDefinitionV3(0xc0000a2000, 0xc0196357a0)
        C:/Users/null/go/pkg/mod/github.com/swaggo/swag/v2@v2.0.0-rc4/parserv3.go:718 +0x405
github.com/swaggo/swag/v2.(*Parser).getTypeSchemaV3(0xc0000a2000, {0xc00051a889, 0x28}, 0xc0001c7860, 0x1)
        C:/Users/null/go/pkg/mod/github.com/swaggo/swag/v2@v2.0.0-rc4/parserv3.go:669 +0xa06
github.com/swaggo/swag/v2.parseObjectSchemaV3(0xc0000a2000, {0xc00051a889, 0x28}, 0xc0001c7860)
        C:/Users/null/go/pkg/mod/github.com/swaggo/swag/v2@v2.0.0-rc4/operationv3.go:851 +0xf9d
github.com/swaggo/swag/v2.(*OperationV3).parseObjectSchema(...)
        C:/Users/null/go/pkg/mod/github.com/swaggo/swag/v2@v2.0.0-rc4/operationv3.go:791
github.com/swaggo/swag/v2.(*OperationV3).parseAPIObjectSchema(0xc01973b000, {0xc00051a87c, 0x35}, {0xc00051a881, 0x6}, {0xc00051a889, 0x28}, 0xc0001c7860)
        C:/Users/null/go/pkg/mod/github.com/swaggo/swag/v2@v2.0.0-rc4/operationv3.go:705 +0x446
github.com/swaggo/swag/v2.(*OperationV3).ParseResponseComment(0xc01973b000, {0xc00051a87c, 0x35}, 0xc0001c7860)
        C:/Users/null/go/pkg/mod/github.com/swaggo/swag/v2@v2.0.0-rc4/operationv3.go:939 +0x13d
github.com/swaggo/swag/v2.(*OperationV3).ParseComment(0xc01973b000, {0xc00051a870?, 0x1?}, 0xc0001c7860)
        C:/Users/null/go/pkg/mod/github.com/swaggo/swag/v2@v2.0.0-rc4/operationv3.go:88 +0x329
github.com/swaggo/swag/v2.(*Parser).ParseRouterAPIInfoV3(0xc0000a2000, 0xc0007cedc0)
        C:/Users/null/go/pkg/mod/github.com/swaggo/swag/v2@v2.0.0-rc4/packages.go:107 +0x33c
        C:/Users/null/go/pkg/mod/github.com/swaggo/swag/v2@v2.0.0-rc4/parser.go:499 +0x63a
github.com/swaggo/swag/v2/gen.(*Gen).Build(0xc0001d5d40, 0xc000128300)
        C:/Users/null/go/pkg/mod/github.com/swaggo/swag/v2@v2.0.0-rc4/gen/gen.go:233 +0x7aa
main.initAction(0xc0001ea380)
        C:/Users/null/go/pkg/mod/github.com/swaggo/swag/v2@v2.0.0-rc4/cmd/swag/main.go:249 +0xa08
github.com/urfave/cli/v2.(*Command).Run(0xc0001c4420, 0xc0001ea380, {0xc000076a20, 0x6, 0x6})
        C:/Users/null/go/pkg/mod/github.com/urfave/cli/v2@v2.25.1/command.go:274 +0x77b
github.com/urfave/cli/v2.(*Command).Run(0xc0001c4840, 0xc0001ea240, {0xc000110000, 0x7, 0x8})
        C:/Users/null/go/pkg/mod/github.com/urfave/cli/v2@v2.25.1/command.go:267 +0x9fc
github.com/urfave/cli/v2.(*App).RunContext(0xc0001ee000, {0x154c0a8, 0x1a31a20}, {0xc000110000, 0x7, 0x8})
        C:/Users/null/go/pkg/mod/github.com/urfave/cli/v2@v2.25.1/app.go:332 +0x566
github.com/urfave/cli/v2.(*App).Run(...)
        C:/Users/null/go/pkg/mod/github.com/urfave/cli/v2@v2.25.1/app.go:309
main.main()
        C:/Users/null/go/pkg/mod/github.com/swaggo/swag/v2@v2.0.0-rc4/cmd/swag/main.go:341 +0x5d8

Code Sample:

type Result[T any] struct {
	Code    Code   `json:"code"`
	Data    T      `json:"data"`
	Message string `json:"message"`
}

type UserInfo struct {
        Id      int    `json:"id"`
}

// List godoc
//
//	@Summary	get list info
//	@Schemes
//	@Description
//	@Tags		test
//	@Accept		json
//	@Produce	json
//	@Success	200	{object}	Result[[]UserInfo]
//	@Router		/list [get]
func List(c *gin.Context) {
        // ...
}

Environment:

• swag version: v2.0.0
• go version: go1.24.0 windows/amd64

Steps to Reproduce:

1. Define a generic type in Go.
2. Annotate a handler function with Swag comments.
3. Run swag init --v3.1 -g handler/handler.go --parseDependency --parseInternal.
   Expected Behavior: Swag should generate the Swagger documentation without errors.

Actual Behavior: Swag panics with a runtime error.

Additional Context: It seems that Swag is unable to correctly parse the generic type. Any guidance or fix for this issue would be appreciated.