Fix Del func

session/bool.go

@@ -25,5 +25,8 @@ func (s *Session) SetBool(name string, value bool) {
 }
 
 func (s *Session) DelBool(name string) {
-	delete(s.varlist.Bool, name)
+	if s.IsSetBool(name) {
+		delete(s.varlist.Bool, name)
+		s.changed = true
+	}
 }

session/int.go

@@ -25,5 +25,8 @@ func (s *Session) SetInt(name string, value int) {
 }
 
 func (s *Session) DelInt(name string) {
-	delete(s.varlist.Int, name)
+	if s.IsSetInt(name) {
+		delete(s.varlist.Int, name)
+		s.changed = true
+	}
 }

session/int64.go

@@ -25,5 +25,8 @@ func (s *Session) SetInt64(name string, value int64) {
 }
 
 func (s *Session) DelInt64(name string) {
-	delete(s.varlist.Int64, name)
+	if s.IsSetInt64(name) {
+		delete(s.varlist.Int64, name)
+		s.changed = true
+	}
 }

session/string.go

@@ -25,5 +25,8 @@ func (s *Session) SetString(name string, value string) {
 }
 
 func (s *Session) DelString(name string) {
-	delete(s.varlist.String, name)
+	if s.IsSetString(name) {
+		delete(s.varlist.String, name)
+		s.changed = true
+	}
 }