Final answer:
Attempting to activate a null reference leads to a runtime error, such as NullPointerException in Java or NullReferenceException in C#. Programmers prevent this by checking for null or using error handling mechanisms.
Step-by-step explanation:
If a program tries to activate a null reference, it will typically result in a runtime error. In object-oriented programming languages, like Java or C#, attempting to access methods or properties of a null object reference will cause a NullPointerException or NullReferenceException, respectively. This occurs because the program attempts to use a reference that does not point to any object in memory, and therefore, cannot perform any actions or retrieve any information.
Handling null references is essential for robust software development, and there are various techniques programmers can use to avoid such errors. They can include checks in their code to ensure that a variable is not null before accessing its methods or properties, use programming constructs designed to handle potential null values safely (such as nullable types and optional or maybe monads), or implement error handling mechanisms to catch and deal with exceptions when they do occur.