Mis on null-viited?

Null reference is a special value indicating the absence of an object that a variable refers to. In most object-oriented programming languages, this value is used to indicate that the reference variable is not linked to any specific instance of a class. Null references are a common source of errors (null pointer exceptions / null reference exceptions), when attempting to access members or methods of an object via a null reference.

Examples in different languages:

// Java
String str = null; // Declaration of null reference
// str.length(); // Will cause NullPointerException

// C#
string name = null; // Declaration of null reference
// name.Length; // Will cause NullReferenceException

# Python
data = None # In Python, similar to null reference, None is used
# data.upper() # Will cause AttributeError

To prevent errors related to null references, various patterns and techniques are used, such as:

• Null check: Explicit check before using the reference.
• Null Object Pattern: Use of a special object that provides "empty" behavior instead of null.
• Optional / Maybe types: Types that explicitly indicate that a value may be absent (e.g., Optional in Java or Maybe in Haskell).
• Annotations: Use of annotations to indicate whether a reference can be null (@Nullable, @NonNull).