Delete if a new specification is nil

Use coalesce for username too.

pkg/cluster/cluster.go

@@ -868,10 +868,9 @@ func (c *Cluster) initSystemUsers() {
 			c.Spec.ConnectionPool = &acidv1.ConnectionPool{}
 		}
 
-		username := c.Spec.ConnectionPool.User
+		username := util.Coalesce(
-		if username == "" {
+			c.Spec.ConnectionPool.User,
-			username = c.OpConfig.ConnectionPool.User
+			c.OpConfig.ConnectionPool.User)
-		}
 
 		c.systemUsers[constants.ConnectionPoolUserKeyName] = spec.PgUser{
 			Origin:   spec.RoleConnectionPool,

pkg/cluster/sync.go

@@ -115,6 +115,14 @@ func (c *Cluster) Sync(newSpec *acidv1.Postgresql) error {
 		oldPool := oldSpec.Spec.ConnectionPool
 		newPool := newSpec.Spec.ConnectionPool
 
+		if newPool == nil {
+			// previously specified connectionPool was removed, so delete
+			// connection pool
+			if err := c.deleteConnectionPool(); err != nil {
+				c.logger.Warningf("could not remove connection pool: %v", err)
+			}
+		}
+
 		// do sync in case if any resources were not remembered (it means they
 		// probably were not created, or if specification differs
 		if c.ConnectionPool == nil ||