The Lear 45 does not have tip tanks. No Learjet model subsequent to the 35/36 does. They were necessary to give these models additional range but at the cost of increased drag and variable roll response/lateral stability characteristics according to the quantity of fuel carried in the tip tanks. Nor are these models as tolerant of fuel imbalance conditions during takeoff and landing as they apparently need to be... (if the accidents attributable to same are any indication)
Pilots who operate these airplanes in a professional manner have fewer such problems of course.