NullReferenceError with DbCommand created before opening Connection

[ThijsKoot]

Issue description

When a DbCommand is created from a connection before the connection has been opened a first time, executing the DbCommand results in a NullReferenceException. This is because the SnowflakeDbCommand-constructor assigns the value of the sfSession-property of SnowflakeDbConnection to itself. The problem here is that sfSession is set when opening the connection, meaning that DbCommand assigns a null value if the connection has never been opened. I'm creating a pull request with a fix for this.

Example code

using (var conn = new SnowflakeDbConnection { ConnectionString = connstr })
{
	var cmd = conn.CreateCommand();
	cmd.CommandText = "select current_version()";
	
	conn.Open();
	
	var result = cmd.ExecuteScalar();
	
	conn.Close();
}

Error log

Not required, problem is in the connector itself.

Configuration

Driver version: 1.1.0

Dotnet framework and version: .net standard 2.0

[ChTimTsubasa]

Thank you for reporting this issue and submitting a PR.