BC32050 Type parameter 'T' .... cannot be inferred

I tried mapping under plain ado.net to object using the excerpt of the code below

calling the code

dim personList as List(of Person) = new List<Person>()
personList = GetList(of Person)(iconn,"persons")

the function

Public Function GetList(Of T As Class)(conn As IDbConnection, tableName As String) As List(Of T)
    ' get body
Using cmd As New MySqlCommand(sql, conn, trans)
        'cmd.Parameters.Add( ,)
        Using rdr = cmd.ExecuteReader()
            ret = MapToObject(rdr) -----> Error line
        End Using
    End Using
    Return ret
' rest of body
End Function

'Map data

Public Function MapToObject(Of T As {Class, New})(dr As IDataReader) As List(Of T)
' Function body
End Function

bu t i get the following error

BC32050 Type parameter 'T' for 'Public Function MapToObject(Of T As {Class, New})(dr As IDataReader) As List(Of T)' cannot be inferred.

Where am i getting it wrong?