Fix errors/panics associated with empty config sections; add warnings…

… when empty sections are found/skipped

control/config.go

@@ -465,6 +465,10 @@ func unmarshalPluginConfig(typ string, p *pluginConfig, t map[string]interface{}
 				switch col := c.(type) {
 				case map[string]interface{}:
 					if v, ok := col["all"]; ok {
+						if v == nil { // handle empty config section by converting nil value to empty map
+							log.WithFields(log.Fields{"name": name, "type": typ}).Warning("Ignoring empty plugin configuration all: section")
+							v = map[string]interface{}{}
+						}
 						jv, err := json.Marshal(v)
 						if err != nil {
 							return err
@@ -489,7 +493,11 @@ func unmarshalPluginConfig(typ string, p *pluginConfig, t map[string]interface{}
 						case map[string]interface{}:
 							for ver, version := range versions {
 								switch v := version.(type) {
-								case map[string]interface{}:
+								case map[string]interface{}, nil:
+									if v == nil { // handle empty config section by converting nil value to empty map
+										log.WithFields(log.Fields{"name": name, "type": typ, "version": ver}).Warning("Ignoring empty plugin configuration version section")
+										v = map[string]interface{}{}
+									}
 									jv, err := json.Marshal(v)
 									if err != nil {
 										return err
@@ -521,6 +529,9 @@ func unmarshalPluginConfig(typ string, p *pluginConfig, t map[string]interface{}
 							return fmt.Errorf("Error unmarshalling %v '%v' expected '%v' got '%v'", typ, name, map[string]interface{}{}, reflect.TypeOf(versions))
 						}
 					}
+				case nil: // ignore empty config section
+					log.WithFields(log.Fields{"name": name, "type": typ}).Warning("Ignoring empty plugin configuration section")
+					continue
 				default:
 					return fmt.Errorf("Error unmarshalling %v '%v' expected '%v' got '%v'", typ, name, map[string]interface{}{}, reflect.TypeOf(col))
 				}

examples/configs/snap-config-empty.yaml

@@ -10,3 +10,8 @@ control:
       psutil:
         all:
           path: /usr/local/bin/psutil
+        # this should not cause a fatal error
+        versions:
+          1:
+      # this should also not cause a fatal error
+      myplugin:

snapteld_test.go

@@ -133,7 +133,7 @@ func TestSnapConfig(t *testing.T) {
 
 func TestSnapConfigEmpty(t *testing.T) {
 	Convey("Test Config", t, func() {
-		Convey("with empty all: plugin config section", func() {
+		Convey("with empty plugin config sections", func() {
 			cfg := getDefaultConfig()
 			readConfig(cfg, "./examples/configs/snap-config-empty.yaml")
 			jb, _ := json.Marshal(cfg)