address code review comments by @graphaelli

beater/handlers.go

@@ -36,7 +36,7 @@ import (
 	conf "github.com/elastic/apm-server/config"
 	"github.com/elastic/apm-server/decoder"
 	"github.com/elastic/apm-server/processor"
-	err "github.com/elastic/apm-server/processor/error"
+	perr "github.com/elastic/apm-server/processor/error"
 	"github.com/elastic/apm-server/processor/metric"
 	"github.com/elastic/apm-server/processor/sourcemap"
 	"github.com/elastic/apm-server/processor/transaction"
@@ -141,8 +141,8 @@ var (
 	ProcessorRoutes = map[string]routeMapping{
 		BackendTransactionsURL:  {backendHandler, transaction.Processor},
 		FrontendTransactionsURL: {frontendHandler, transaction.Processor},
-		BackendErrorsURL:        {backendHandler, err.Processor},
-		FrontendErrorsURL:       {frontendHandler, err.Processor},
+		BackendErrorsURL:        {backendHandler, perr.Processor},
+		FrontendErrorsURL:       {frontendHandler, perr.Processor},
 		MetricsURL:              {metricsHandler, metric.Processor},
 		SourcemapsURL:           {sourcemapHandler, sourcemap.Processor},
 	}

model/metric/payload_test.go

@@ -251,10 +251,10 @@ func TestPayloadDecode(t *testing.T) {
 	} {
 		payloadInterface, err := DecodePayload(test.input)
 
-		// its ok to ignore the outcome of this cast here because
-		// we assert everything below
 		payload, ok := payloadInterface.(*Payload)
-		require.True(t, ok)
+		if payloadInterface != nil {
+			require.True(t, ok)
+		}
 
 		// compare metrics separately as they may be ordered differently
 		if test.p != nil && test.p.Metrics != nil {