Make sure to generate UUIDs when services are registered without one

This makes the behavior line up with the docs and expected behavior

agent/catalog_endpoint_test.go

@@ -8,9 +8,11 @@ import (
 	"time"
 
 	"github.com/hashicorp/consul/agent/structs"
+   "github.com/hashicorp/consul/types"
 	"github.com/hashicorp/consul/testutil/retry"
 	"github.com/hashicorp/serf/coordinate"
 	"github.com/stretchr/testify/assert"
+   "github.com/stretchr/testify/require"
 )
 
 func TestCatalogRegister_Service_InvalidAddress(t *testing.T) {
@@ -109,6 +111,34 @@ func TestCatalogNodes(t *testing.T) {
 	}
 }
 
+func TestCatalog_RegisterNoID(t *testing.T) {
+   t.Parallel()
+   a := NewTestAgent(t.Name(), "")
+   defer a.Shutdown()
+
+   // Register node
+   args := &structs.RegisterRequest{
+      Datacenter: "dc1",
+      Node:       "foo",
+      Address:    "127.0.0.1",
+   }
+
+   var out struct{}
+   require.NoError(t, a.RPC("Catalog.Register", args, &out))
+
+   req, _ := http.NewRequest("GET", "/v1/catalog/node/foo", nil)
+   resp := httptest.NewRecorder()
+   obj, err := a.srv.CatalogNodeServices(resp, req)
+   require.NoError(t, err)
+
+   // Verify an index is set
+   assertIndex(t, resp)
+
+   node := obj.(*structs.NodeServices)
+   
+   require.NotEqual(t, types.NodeID(""), node.Node.ID)
+}
+
 func TestCatalogNodes_MetaFilter(t *testing.T) {
 	t.Parallel()
 	a := NewTestAgent(t.Name(), "")

agent/consul/catalog_endpoint.go

@@ -37,7 +37,15 @@ func (c *Catalog) Register(args *structs.RegisterRequest, reply *struct{}) error
 		if _, err := uuid.ParseUUID(string(args.ID)); err != nil {
 			return fmt.Errorf("Bad node ID: %v", err)
 		}
-	}
+	} else {
+      id, err := uuid.GenerateUUID()
+      if err != nil {
+         return fmt.Errorf("Failed to generate ID: %v", err)
+      }
+      
+      args.ID = types.NodeID(id)
+   }
+
 
 	// Fetch the ACL token, if any.
 	rule, err := c.srv.resolveToken(args.Token)