This is happening on dev:

Caught panic during handling of "/_ah/push-handlers/buildbot": unknown status 5
goroutine 2762 [running]:
go.chromium.org/luci/common/runtime/paniccatcher.Catch(0xc017f15108)
	go.chromium.org/luci/common/runtime/paniccatcher/catch.go:41 +0xb9
panic(0x158e200, 0xc0166da880)
	go/src/runtime/panic.go:443 +0x4e9
go.chromium.org/luci/milo/api/buildbot.Result.Status(0x5, 0x50)
	go.chromium.org/luci/milo/api/buildbot/result.go:55 +0x17b
go.chromium.org/luci/milo/buildsource/buildbot.summary(0x2b2c3b970840, 0xc012da0f90, 0xc012d96dc0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, 0x0, ...)
	go.chromium.org/luci/milo/buildsource/buildbot/build.go:75 +0xe46
go.chromium.org/luci/milo/buildsource/buildbot.renderBuild(0x2b2c3b970840, 0xc012da0f90, 0xc012d96dc0, 0x0)
	go.chromium.org/luci/milo/buildsource/buildbot/build.go:402 +0x85
go.chromium.org/luci/milo/buildsource/buildbot.saveBuildSummary(0x2b2c3b970840, 0xc012da0f90, 0xc012d96dc0, 0x0, 0x0)
	go.chromium.org/luci/milo/buildsource/buildbot/pubsub.go:152 +0x5f
go.chromium.org/luci/milo/buildsource/buildbot.pubSubHandlerImpl(0x2b2c3b970840, 0xc012da0f90, 0xc0185181c0, 0x8)
	go.chromium.org/luci/milo/buildsource/buildbot/pubsub.go:301 +0x19cb
go.chromium.org/luci/milo/buildsource/buildbot.PubSubHandler(0xc011f34c80)
	go.chromium.org/luci/milo/buildsource/buildbot/pubsub.go:190 +0x36
go.chromium.org/luci/server/router.run(0xc011f34c80, 0x0, 0x0, 0x0, 0xc010568e68, 0x0, 0x0, 0x1b72d88)
	go.chromium.org/luci/server/router/handler.go:95 +0x383
go.chromium.org/luci/server/router.run.func2(0xc011f34c80)
	go.chromium.org/luci/server/router/handler.go:90 +0x7e
go.chromium.org/luci/server/templates.WithTemplates.func1(0xc011f34c80, 0xc012da0f60)
	go.chromium.org/luci/server/templates/middleware.go:36 +0x202
go.chromium.org/luci/server/router.run(0xc011f34c80, 0x0, 0x0, 0x0, 0xc010568e68, 0x1, 0x1, 0x1b72d88)
	go.chromium.org/luci/server/router/handler.go:90 +0x2b5
go.chromium.org/luci/server/router.run.func2(0xc011f34c80)
	go.chromium.org/luci/server/router/handler.go:90 +0x7e
go.chromium.org/luci/milo/frontend.withRequestMiddleware(0xc011f34c80, 0xc012da0f00)
	go.chromium.org/luci/milo/frontend/middleware.go:358 +0x19a
go.chromium.org/luci/server/router.run(0xc011f34c80, 0x0, 0x0, 0x0, 0xc010568e60, 0x2, 0x2, 0x1b72d88)
	go.chromium.org/luci/server/router/handler.go:90 +0x2b5
go.chromium.org/luci/server/router.run.func2(0xc011f34c80)
	go.chromium.org/luci/server/router/handler.go:90 +0x7e
go.chromium.org/luci/server/auth.(*Authenticator).GetMiddleware.func1(0xc011f34c80, 0xc012e0ac90)
	go.chromium.org/luci/server/auth/auth.go:137 +0x17e
go.chromium.org/luci/server/router.run(0xc011f34c80, 0x0, 0x0, 0x0, 0xc010568e58, 0x3, 0x3, 0x1b72d88)
	go.chromium.org/luci/server/router/handler.go:90 +0x2b5
go.chromium.org/luci/server/router.run.func2(0xc011f34c80)
	go.chromium.org/luci/server/router/handler.go:90 +0x7e
go.chromium.org/luci/appengine/tsmon.(*State).Middleware(0x20ec960, 0xc011f34c80, 0xc012e0ab40)
	go.chromium.org/luci/appengine/tsmon/middleware.go:116 +0x37d
go.chromium.org/luci/appengine/tsmon.(*State).Middleware-fm(0xc011f34c80, 0xc012e0ab40)
	go.chromium.org/luci/appengine/gaemiddleware/standard/env.go:81 +0x34
go.chromium.org/luci/server/router.run(0xc011f34c80, 0x0, 0x0, 0x0, 0xc010568e50, 0x4, 0x4, 0x1b72d88)
	go.chromium.org/luci/server/router/handler.go:90 +0x2b5
go.chromium.org/luci/server/router.run.func2(0xc011f34c80)
	go.chromium.org/luci/server/router/handler.go:90 +0x7e
go.chromium.org/luci/server/middleware.WithPanicCatcher(0xc011f34c80, 0xc012e0ab10)
	go.chromium.org/luci/server/middleware/paniccatcher.go:42 +0xc5
go.chromium.org/luci/server/router.run(0xc011f34c80, 0x0, 0x0, 0x0, 0xc010568e48, 0x5, 0x5, 0x1b72d88)
	go.chromium.org/luci/server/router/handler.go:90 +0x2b5
go.chromium.org/luci/server/router.run.func2(0xc011f34c80)
	go.chromium.org/luci/server/router/handler.go:90 +0x7e
go.chromium.org/luci/appengine/gaemiddleware.(*Environment).Base.func1(0xc011f34c80, 0xc01a7abe30)
	go.chromium.org/luci/appengine/gaemiddleware/context.go:201 +0x10b
go.chromium.org/luci/server/router.run(0xc011f34c80, 0x0, 0x0, 0x0, 0xc010568e40, 0x6, 0x6, 0x1b72d88)
	go.chromium.org/luci/server/router/handler.go:90 +0x2b5
go.chromium.org/luci/server/router.runChains(0xc011f34c80, 0x0, 0x0, 0x0, 0xc010568e40, 0x6, 0x6, 0x1b72d88)
	go.chromium.org/luci/server/router/handler.go:74 +0x6e
go.chromium.org/luci/server/router.(*Router).adapt.func1(0x2b2c3b970798, 0xc018007e80, 0xc0185181c0, 0x0, 0x0, 0x0)
	go.chromium.org/luci/server/router/router.go:147 +0x178
github.com/julienschmidt/httprouter.(*Router).ServeHTTP(0xc01069dd00, 0x2b2c3b970798, 0xc018007e80, 0xc0185181c0)
	github.com/julienschmidt/httprouter/router.go:344 +0x195
go.chromium.org/luci/server/router.(*Router).ServeHTTP(0xc010568990, 0x2b2c3b970798, 0xc018007e80, 0xc0185181c0)
	go.chromium.org/luci/server/router/router.go:118 +0x42
net/http.(*ServeMux).ServeHTTP(0xc010434b70, 0x2b2c3b970798, 0xc018007e80, 0xc0185181c0)
	go/src/net/http/server.go:1910 +0x17d
appengine_internal.executeRequestSafely(0xc018007e80, 0xc0185181c0)
	go/src/appengine_internal/api_prod.go:304 +0x8d
appengine_internal.(*server).HandleRequest(0x20e6cd0, 0xc0105259e0, 0xc0174be180, 0xc0138814a0, 0x0, 0x0)
	go/src/appengine_internal/api_prod.go:238 +0x15c6
reflect.Value.call(0x167e5e0, 0x20e6cd0, 0x213, 0x18556b8, 0x4, 0xc017f15f20, 0x3, 0x3, 0x0, 0x0, ...)
	go/src/reflect/value.go:435 +0x120d
reflect.Value.Call(0x167e5e0, 0x20e6cd0, 0x213, 0xc017f15f20, 0x3, 0x3, 0x0, 0x0, 0x0)
	go/src/reflect/value.go:303 +0xb1