but in runtime it prints that result is null, that’s what I’m saying

Maybe because in Java when a String is

null

and is treated as

"null"

if we apply String operations other than condition checking For eg in Java:

String s1 = null;
String s2 = "test";
String s3 = s1 + s2;
System.out.println(s3);

The above snippet prints

nulltest

.