Fix null value when adding expression col to fields on pgsql

store/mysql/upgrade.go

@@ -176,6 +176,10 @@ func (u upgrader) AddColumn(ctx context.Context, table string, col *ddl.Column)
 			return nil
 		}
 
+		if col.Type.Type == ddl.ColumnTypeText || col.Type.Type == ddl.ColumnTypeJson {
+			col.DefaultValue = ""
+		}
+
 		if err = u.Exec(ctx, u.ddl.AddColumn(table, col)); err != nil {
 			return err
 		}

store/rdbms/generic_upgrades.go

@@ -366,7 +366,12 @@ func (g genericUpgrades) AlterComposeModuleRenameJsonToMeta(ctx context.Context)
 
 func (g genericUpgrades) AlterComposeModuleFieldAddExpresions(ctx context.Context) (err error) {
 	var (
-		col = &ddl.Column{Name: "expressions", Type: ddl.ColumnType{Type: ddl.ColumnTypeJson}, IsNull: false}
+		col = &ddl.Column{
+			Name:         "expressions",
+			Type:         ddl.ColumnType{Type: ddl.ColumnTypeJson},
+			IsNull:       false,
+			DefaultValue: "'{}'",
+		}
 	)
 
 	_, err = g.u.AddColumn(ctx, "compose_module_field", col)