how to generate null pointer check in simulink model

i'm converting C code into Matlab simulink model. How can I implement NULL pointer check in simulink model and generate codes that does NULL pointer test?

How to generate this if(var1 != NULL_PTR) in simulink model and generate code similarly from model.

void sample(uint8 *var1) 
{ 
  if(var1 != NULL_PTR)
  { 
    /* Do Something */
  } 
}