{"id":"1f4d33d6d4962a89","repo":"gofiber/fiber","slug":"route-handler-fn-cannot-be-nil-1f4d33","errorCode":null,"errorMessage":"route handler 'fn' cannot be nil","messagePattern":"route handler 'fn' cannot be nil","errorType":"panic","errorClass":null,"httpStatus":null,"severity":"error","filePath":"group.go","lineNumber":243,"sourceCode":"\t\tmatcher: parseDomainPattern(host),\n\t}\n}\n\n// RouteChain creates a Registering instance scoped to the group's prefix,\n// allowing chained route declarations for the same path.\nfunc (grp *Group) RouteChain(path string) Register {\n\t// Create new group\n\tregister := &Registering{app: grp.app, group: grp, path: getGroupPath(grp.Prefix, path)}\n\n\treturn register\n}\n\n// Route is used to define routes with a common prefix inside the supplied\n// function. It mirrors the legacy helper and reuses the Group method to create\n// a sub-router.\nfunc (grp *Group) Route(prefix string, fn func(router Router), name ...string) Router {\n\tif fn == nil {\n\t\tpanic(\"route handler 'fn' cannot be nil\")\n\t}\n\t// Create new group\n\tgroup := grp.Group(prefix)\n\tif len(name) > 0 {\n\t\tgroup.Name(name[0])\n\t}\n\n\t// Define routes\n\tfn(group)\n\n\treturn group\n}\n","sourceCodeStart":225,"sourceCodeEnd":256,"githubUrl":"https://github.com/gofiber/fiber/blob/9a4c7e57fe0b080a04235d28a4b0d2b4b353d58c/group.go#L225-L256","documentation":"Group.Route creates a sub-router under a prefix and invokes the supplied function to register routes on it. Passing nil is a programming error with nothing to execute, so it panics with \"route handler 'fn' cannot be nil\". This mirrors the same guard on domainRouter.Route.","triggerScenarios":"Calling grp.Route(\"/api\", nil), or passing a function variable that is nil because a registration function was looked up but not found.","commonSituations":"Splitting routes into files and forgetting to assign the registration function in one file. Conditionally registering routes and passing nil in the else branch. Refactoring that leaves a dangling nil.","solutions":["Pass a non-nil func(router Router) that registers the sub-routes.","Guard optional route groups with an if instead of passing nil.","Initialize registration variables at declaration so they cannot be nil at call time."],"exampleFix":"// before\ngrp.Route(\"/api\", nil)\n// after\ngrp.Route(\"/api\", func(r fiber.Router) {\n    r.Get(\"/items\", listItems)\n})","handlingStrategy":"validation","validationCode":"if fn == nil {\n    log.Fatal(\"group: Route requires a non-nil registration function\")\n}\ngrp.Route(\"/api\", fn)","typeGuard":null,"tryCatchPattern":null,"preventionTips":["Pass a func literal directly to Route to avoid nil variables.","Initialize route-registration functions at declaration in their source files."],"tags":["routing","group","handler","panic"],"analyzedSha":"9a4c7e57fe0b080a04235d28a4b0d2b4b353d58c","analyzedAt":"2026-08-04T21:44:03.395Z","schemaVersion":2}