Per https://github.com/dotnet/runtime/issues/509#issuecomment-677516936, `GetSchemaTable` should return `null` when there is no result set. This reverts part of https://github.com/mysql-net/MySqlConnector/issues/744.
Per dotnet/runtime#509 (comment),
GetSchemaTableshould returnnullwhen there is no result set. This reverts part of #744.