{"record":{"id":"a427a551eea7adf5","repo":"gofiber/fiber","slug":"nil-handler-in-route-s","errorCode":null,"errorMessage":"nil handler in route: %s\n","messagePattern":"nil handler in route: (.+?)\n","errorType":"panic","errorClass":null,"httpStatus":null,"severity":"error","filePath":"router.go","lineNumber":1003,"sourceCode":"\t\t\tcontinue\n\t\t}\n\n\t\tapp.stack[headIndex] = append(headStack[:i], headStack[i+1:]...)\n\t\tapp.hasRoutesRefreshed = true\n\t\tatomic.AddUint32(&app.handlersCount, ^uint32(len(headRoute.Handlers)-1)) //nolint:gosec // G115 - handler count is always small\n\t\treturn\n\t}\n}\n\nfunc (app *App) register(methods []string, pathRaw string, group *Group, handlers ...Handler) {\n\t// A regular route requires at least one ctx handler\n\tif len(handlers) == 0 && group == nil {\n\t\tpanic(fmt.Sprintf(\"missing handler/middleware in route: %s\\n\", pathRaw))\n\t}\n\t// No nil handlers allowed\n\tfor _, h := range handlers {\n\t\tif h == nil {\n\t\t\tpanic(fmt.Sprintf(\"nil handler in route: %s\\n\", pathRaw))\n\t\t}\n\t}\n\n\t// Precompute path normalization ONCE\n\tif pathRaw == \"\" {\n\t\tpathRaw = \"/\"\n\t}\n\tif pathRaw[0] != '/' {\n\t\tpathRaw = \"/\" + pathRaw\n\t}\n\tpathPretty := pathRaw\n\tif !app.config.CaseSensitive {\n\t\tpathPretty = utilsstrings.ToLower(pathPretty)\n\t}\n\tif !app.config.StrictRouting && len(pathPretty) > 1 {\n\t\tpathPretty = utils.TrimRight(pathPretty, '/')\n\t}\n\tpathClean := RemoveEscapeChar(pathPretty)","sourceCodeStart":985,"sourceCodeEnd":1021,"githubUrl":"https://github.com/gofiber/fiber/blob/a105acad6c1e4576a77f01e02973f67e962bb58d/router.go#L985-L1021","documentation":"register iterates every handler passed to a route registration and panics if any is nil. A nil handler would later panic inside the router when invoked, so this guard surfaces the mistake at startup with the offending path. This is distinct from the \"missing handler\" check: here handlers were provided, but one of them is a nil function value.","triggerScenarios":"app.Get(\"/x\", h1, nil, h3) where a handler variable was never assigned; passing a nil element from a handler slice; a middleware factory that returned nil on a misconfiguration.","commonSituations":"A handler variable conditionally assigned that stayed nil; a slice of middleware where one entry was nil; refactoring that left a placeholder nil in a chain; appending middleware that was supposed to be constructed but was not.","solutions":["Ensure every handler/middleware value is non-nil before passing it to a registration method.","If a middleware is optional, conditionally append it rather than inserting nil, or substitute a no-op handler.","Lint for nil-typed handler variables in route-building code."],"exampleFix":"// before\nvar auth fiber.Handler // nil when not configured\napp.Get(\"/secret\", auth, handler) // panics: nil handler\n\n// after\napp.Get(\"/secret\", handler)\nif auth != nil {\n    app.Get(\"/secret\", auth, handler)\n}","handlingStrategy":"type-guard","validationCode":"func cleanHandlers(handlers ...fiber.Handler) []fiber.Handler {\n    out := make([]fiber.Handler, 0, len(handlers))\n    for _, h := range handlers {\n        if h != nil { out = append(out, h) }\n    }\n    return out\n}\n// app.Get(\"/x\", cleanHandlers(h1, h2)...)","typeGuard":"func noNilHandlers(handlers []fiber.Handler) bool {\n    for _, h := range handlers { if h == nil { return false } }\n    return true\n}","tryCatchPattern":null,"preventionTips":["Never insert nil as a placeholder in a handler chain — substitute a no-op fiber.Handler or conditionally append.","Lint for handler variables that may be nil at the point of registration.","Initialize handler variables at declaration rather than in a conditional that might not run."],"tags":["router","config","panic","routing","nil-safety"],"backgroundTag":null,"analyzedSha":"a105acad6c1e4576a77f01e02973f67e962bb58d","analyzedAt":"2026-08-11T17:33:26.942Z","contentChangedAt":null,"schemaVersion":2},"datasetVersion":"2026-09-23T08:17:48.524Z"}