renameColumn: non-null column can't default null

lib/query-interface.js

@@ -400,6 +400,11 @@ module.exports = (function() {
           defaultValue: data.defaultValue
           defaultValue: data.defaultValue
         }
         }
 
 
+        // fix: a not-null column cannot have null as default value
+        if (data.defaultValue === null && !data.allowNull) {
+          delete options[attrNameAfter].defaultValue;
+        }
+
         if (this.sequelize.options.dialect === 'sqlite') {
         if (this.sequelize.options.dialect === 'sqlite') {
           // sqlite needs some special treatment as it cannot rename a column
           // sqlite needs some special treatment as it cannot rename a column
           SQLiteQueryInterface.renameColumn.call(this, tableName, attrNameBefore, attrNameAfter, emitter, queryAndEmit)
           SQLiteQueryInterface.renameColumn.call(this, tableName, attrNameBefore, attrNameAfter, emitter, queryAndEmit)