[FAB-8027] Check for empty channel group

Although any well formed channel config will have a non-empty channel
group, the config update computation code should not assume that it is
well formed.  This CR simply adds nil checking over the channel group
fields.

Change-Id: I9a470d5cf6a559be1bcbbbdf919ac5670c90da1a
Signed-off-by: Jason Yellick <jyellick@us.ibm.com>

common/tools/configtxlator/update/update.go

@@ -223,6 +223,14 @@ func computeGroupUpdate(original, updated *cb.ConfigGroup) (readSet, writeSet *c
 }
 
 func Compute(original, updated *cb.Config) (*cb.ConfigUpdate, error) {
+	if original.ChannelGroup == nil {
+		return nil, fmt.Errorf("no channel group included for original config")
+	}
+
+	if updated.ChannelGroup == nil {
+		return nil, fmt.Errorf("no channel group included for updated config")
+	}
+
 	readSet, writeSet, groupUpdated := computeGroupUpdate(original.ChannelGroup, updated.ChannelGroup)
 	if !groupUpdated {
 		return nil, fmt.Errorf("no differences detected between original and updated config")

common/tools/configtxlator/update/update_test.go

@@ -39,6 +39,22 @@ func TestNoUpdate(t *testing.T) {
 	assert.Error(t, err)
 }
 
+func TestMissingGroup(t *testing.T) {
+	group := &cb.ConfigGroup{}
+	t.Run("MissingOriginal", func(t *testing.T) {
+		_, err := Compute(&cb.Config{}, &cb.Config{ChannelGroup: group})
+
+		assert.Error(t, err)
+		assert.Regexp(t, "no channel group included for original config", err.Error())
+	})
+	t.Run("MissingOriginal", func(t *testing.T) {
+		_, err := Compute(&cb.Config{ChannelGroup: group}, &cb.Config{})
+
+		assert.Error(t, err)
+		assert.Regexp(t, "no channel group included for updated config", err.Error())
+	})
+}
+
 func TestGroupModPolicyUpdate(t *testing.T) {
 	original := &cb.ConfigGroup{
 		Version:   7,