Refactor null-checking code.

Eliminate 'session' local variable that was only used to access the Id, and store that in a local instead. (This mostly reverts changes from eadb98c and restores the code to how it was in 2f0e81c.)

Use more pattern matching to check for null and avoid reading fields twice.

Author: bgrainger

src/MySqlConnector/MySqlConnection.cs

@@ -746,14 +746,13 @@ internal ServerSession Session
 
 	internal void Cancel(ICancellableCommand command, int commandId, bool isCancel)
 	{
-		var session = m_session;
-		if (session is null || State != ConnectionState.Open || !session.TryStartCancel(command))
+		if (m_session?.Id is not string sessionId || State != ConnectionState.Open || m_session?.TryStartCancel(command) is not true)
 		{
 			Log.Trace("Ignoring cancellation for closed connection or invalid CommandId {0}", commandId);
 			return;
 		}
 
-		Log.Debug("CommandId {0} for Session{1} has been canceled via {2}.", commandId, session.Id, isCancel ? "Cancel()" : "command timeout");
+		Log.Debug("CommandId {0} for Session{1} has been canceled via {2}.", commandId, sessionId, isCancel ? "Cancel()" : "command timeout");
 
 		try
 		{
@@ -763,8 +762,8 @@ internal void Cancel(ICancellableCommand command, int commandId, bool isCancel)
 				AutoEnlist = false,
 				Pooling = false,
 			};
-			if (session.IPAddress is not null)
-				csb.Server = session.IPAddress.ToString();
+			if (m_session?.IPAddress is { } ipAddress)
+				csb.Server = ipAddress.ToString();
 			var cancellationTimeout = GetConnectionSettings().CancellationTimeout;
 			csb.ConnectionTimeout = cancellationTimeout < 1 ? 3u : (uint) cancellationTimeout;
 
@@ -778,13 +777,13 @@ internal void Cancel(ICancellableCommand command, int commandId, bool isCancel)
 		{
 			// ignore a rare race condition where the connection is open at the beginning of the method, but closed by the time
 			// KILL QUERY is executed: https://github.com/mysql-net/MySqlConnector/issues/1002
-			Log.Info(ex, "Session{0} ignoring cancellation for closed connection.", session.Id);
+			Log.Info(ex, "Session{0} ignoring cancellation for closed connection.", sessionId);
 			m_session?.AbortCancel(command);
 		}
 		catch (MySqlException ex)
 		{
 			// cancelling the query failed; setting the state back to 'Querying' will allow another call to 'Cancel' to try again
-			Log.Info(ex, "Session{0} cancelling CommandId {1} failed", session.Id, command.CommandId);
+			Log.Info(ex, "Session{0} cancelling CommandId {1} failed", sessionId, command.CommandId);
 			m_session?.AbortCancel(command);
 		}
 	}