Don't use pointer to interface (#465)

Minor fix. Interfaces can be nil, so there is no need for the extra
pointer to interface.

pkg/api/payer/publish_test.go

@@ -75,17 +75,15 @@ func buildPayerService(
 	mockMessagePublisher := blockchainMocks.NewMockIBlockchainPublisher(t)
 
 	metaMocks := metadataMocks.NewMockMetadataApiClient(t)
-	metadataConstructor := &FixedMetadataApiClientConstructor{
-		mockClient: metaMocks,
-	}
-	var interf payer.MetadataApiClientConstructor = metadataConstructor
 	payerService, err := payer.NewPayerApiService(
 		ctx,
 		log,
 		mockRegistry,
 		privKey,
 		mockMessagePublisher,
-		&interf,
+		&FixedMetadataApiClientConstructor{
+			mockClient: metaMocks,
+		},
 	)
 	require.NoError(t, err)
 

pkg/api/payer/service.go

@@ -41,14 +41,14 @@ func NewPayerApiService(
 	registry registry.NodeRegistry,
 	payerPrivateKey *ecdsa.PrivateKey,
 	blockchainPublisher blockchain.IBlockchainPublisher,
-	metadataApiClient *MetadataApiClientConstructor,
+	metadataApiClient MetadataApiClientConstructor,
 ) (*Service, error) {
 	var metadataClient MetadataApiClientConstructor
 	clientManager := NewClientManager(log, registry)
 	if metadataApiClient == nil {
 		metadataClient = &DefaultMetadataApiClientConstructor{clientManager: clientManager}
 	} else {
-		metadataClient = *metadataApiClient
+		metadataClient = metadataApiClient
 	}
 	return &Service{
 		ctx:                 ctx,