v1.6.8 External package is not going to be resolved

[Rayer]

Describe the bug
After upgrade v1.6.8, external package struct can't be resolved correctly, and product error.

To Reproduce
Here is an sample code

// IssueApiKey godoc
// @Summary Issue an API Key
// @Description Issue an API Key to user, this endpoint requires privileges
// @Tags ApiKey
// @Accept json
// @Produce json
// @param input body IssueApiKeyPayload true "Input info"
// @Param apiKey query string true "API Key(Privileged)"
// @Security ApiKeyAuth
// @Success 200 {object} IssueApiKeyResponse
// @Failure 400 {object} problems.DefaultProblem
// @Router /apiKey [post]
func (c *Controller) IssueApiKey(ctx *gin.Context) {
	input := &IssueApiKeyPayload{}
	err := ctx.BindJSON(input)
	if err != nil {
		err400 := problems.NewDetailedProblem(http.StatusBadRequest, err.Error())
		ctx.JSON(400, err400)
		return
	}
	key, err := c.ApiKeyService.IssueApiKey(input.Application, input.UseInHeader, input.UseInQueryParam, "auto", false)
	if err != nil {
		err500 := problems.NewDetailedProblem(http.StatusInternalServerError, err.Error())
		ctx.JSON(500, err500)
		return
	}
	ctx.JSON(http.StatusOK, IssueApiKeyResponse{
		Key: key,
	})
}

in v1.6.7, it works fine. In v1.6.8, it products error

2020/10/16 15:19:43 Generate swagger docs....
2020/10/16 15:19:43 Generate general API Info, search dir:./
2020/10/16 15:19:44 Generating main.IssueApiKeyPayload
2020/10/16 15:19:44 Generating main.IssueApiKeyResponse
2020/10/16 15:19:44 ParseComment error in file apikey_controller.go :cannot find type definition: problems.DefaultProblem
server_main.go:26: running "/Users/killercat/go/bin/swag": exit status 1

problems.DefaultProblem is defined in external library, for this case, it's https://github.com/mschneider82/problem

Expected behavior
It should able to generate swagger.json in this case in v1.6.7. It's broken in v1.6.8

Screenshots

Your swag version
e.g. 1.6.8

Your go version
e.g. 1.15.1

Desktop (please complete the following information):

• OS: macOS 10.15.7
• Browser: Safari

Additional context
None

[Rayer]

Properly duplicated with #802

[Rayer]

It seems author have explained in #808, close this ticket.