Fix support for Npgsql6 provider (#3064)

Author: hazzik

src/NHibernate/Driver/NpgsqlDriver.cs

@@ -65,19 +65,33 @@ public override IResultSetsCommand GetResultSetsCommand(Engine.ISessionImplement
 
 		protected override void InitializeParameter(DbParameter dbParam, string name, SqlTypes.SqlType sqlType)
 		{
-			base.InitializeParameter(dbParam, name, sqlType);
+			if (sqlType == null)
+				throw new QueryException($"No type assigned to parameter '{name}'");
 
-			// Since the .NET currency type has 4 decimal places, we use a decimal type in PostgreSQL instead of its native 2 decimal currency type.
+			dbParam.ParameterName = FormatNameForParameter(name);
 			if (sqlType.DbType == DbType.Currency)
+			{
+				// Since the .NET currency type has 4 decimal places, we use a decimal type in PostgreSQL instead of its native 2 decimal currency type.
 				dbParam.DbType = DbType.Decimal;
+			}
+			else if (DriverVersionMajor < 6 || sqlType.DbType != DbType.DateTime)
+			{
+				dbParam.DbType = sqlType.DbType;
+			}
+			else
+			{
+				// Let Npgsql 6 driver to decide parameter type 
+			}
 		}
 
 		// Prior to v3, Npgsql was expecting DateTime for time.
 		// https://github.com/npgsql/npgsql/issues/347
-		public override bool RequiresTimeSpanForTime => (DriverVersion?.Major ?? 3) >= 3;
+		public override bool RequiresTimeSpanForTime => DriverVersionMajor >= 3;
 
 		public override bool HasDelayedDistributedTransactionCompletion => true;
 
 		System.Type IEmbeddedBatcherFactoryProvider.BatcherFactoryClass => typeof(GenericBatchingBatcherFactory);
+
+		private int DriverVersionMajor => DriverVersion?.Major ?? 3;
 	}
 }