Assertion coverage

Coverage
1

Hi,

I gave an assertion in test case like this :

for(i=0;i<10;i++;) begin
  if(reg == NULL) begin
    assert(error == 2)else $error("");
  end
  else begin
   //some statements
  end
 end

but in coverage the same assertion line has been showed two times once covering and other time not covering can someone please answer