added if statement to avoid null values

src/userprog/process.c

@@ -70,10 +70,15 @@ process_execute (const char *file_name)
     //prints out to check the args 
     
     printf("filename: %s\n", filename);
-  
+      if(args1!=NULL){
           printf("args1: %s\n", args1);
+      }
+      if(args2!=NULL){
           printf("args2: %s\n", args2);
+      }
+      if(args3!=NULL){
           printf("args3: %s\n", args3);
+      }