Optimize the code

Src/Asp.Net/SqlSugar/Abstract/InsertableProvider/InsertableProvider.cs

@@ -320,6 +320,7 @@ namespace SqlSugar
         }
         public IInsertable<T> IgnoreColumns(Expression<Func<T, object>> columns)
         {
+            if (columns == null) return this;
             var ignoreColumns = InsertBuilder.GetExpressionValue(columns, ResolveExpressType.ArraySingle).GetResultArray().Select(it => this.SqlBuilder.GetNoTranslationColumnName(it)).ToList();
             this.InsertBuilder.DbColumnInfoList = this.InsertBuilder.DbColumnInfoList.Where(it => !ignoreColumns.Any(ig => ig.Equals(it.PropertyName, StringComparison.CurrentCultureIgnoreCase))).ToList();
             this.InsertBuilder.DbColumnInfoList = this.InsertBuilder.DbColumnInfoList.Where(it => !ignoreColumns.Any(ig => ig.Equals(it.DbColumnName, StringComparison.CurrentCultureIgnoreCase))).ToList();