Specman - Error: Cannot access null port expression - specman

Question

I have a monitor unit with the following fields/events:
uart_env.e:
unit uart_monitor_u like uvm_monitor{
smp : uart_signal_map_u; //ptr to smp
keep smp == get_enclosing_unit(uart_env_u).smp;
kind : uart_monitor_u_kind_t;
};
uart_monitor.e:
extend uart_monitor_u{
!port_data_b : inout simple_port of bit; -- pointer to the data-bit port
event clk_e is rise (smp.port_uart_clk$) #sim;
event data_deassert is fall (port_data_b$) #uart_clk_e;
.......
.......
};
uart_rx_monitor.e:
extend RX uart_monitor_u{
keep soft port_data_b == smp.port_rxdi;
.....
.....
};
uart_types.e:
type uart_monitor_u_kind_t: [ RX, TX ];
uart_signal_map.e:
extend uart_signal_map_u {
p_def port_uart_clk bit;
p_def port_uart_clk_period real;
p_def port_resetn bit;
p_def port_br_clk_period real;
p_def port_uart_int bit;
p_def port_txdo bit;
p_def port_rxdi bit;
......
......
};
The order of the compilation of the relevant file:
import uart_types;
import uart_env;
import uart_monitor;
import uart_rx_monitor;
For some reason I got the following error when I try to compile:
*** Error: Cannot access null port expression.
at line 22 in #uart_monitor
event data_deassert is fall (port_data_b$) #uart_clk_e;

Answer 1

the port_data_b pointer is marked as do-not-generate. so it remains NULL.
try removing the "!" from it