libs/common: refactor libs common 3 (#4232)

* libs/common: refactor libs common 3

- move nil.go into types folder and make private
- move service & baseservice out of common into service pkg

ref #4147

Signed-off-by: Marko Baricevic <marbar3778@yahoo.com>

* add changelog entry

types/utils.go

@@ -0,0 +1,29 @@
+package types
+
+import "reflect"
+
+// Go lacks a simple and safe way to see if something is a typed nil.
+// See:
+//  - https://dave.cheney.net/2017/08/09/typed-nils-in-go-2
+//  - https://groups.google.com/forum/#!topic/golang-nuts/wnH302gBa4I/discussion
+//  - https://github.com/golang/go/issues/21538
+func isTypedNil(o interface{}) bool {
+	rv := reflect.ValueOf(o)
+	switch rv.Kind() {
+	case reflect.Chan, reflect.Func, reflect.Map, reflect.Ptr, reflect.Slice:
+		return rv.IsNil()
+	default:
+		return false
+	}
+}
+
+// Returns true if it has zero length.
+func isEmpty(o interface{}) bool {
+	rv := reflect.ValueOf(o)
+	switch rv.Kind() {
+	case reflect.Array, reflect.Chan, reflect.Map, reflect.Slice, reflect.String:
+		return rv.Len() == 0
+	default:
+		return false
+	}
+}