What does a 'NullReferenceError' mean in Godot, and how can I fix it?

A NullReferenceError occurs when you try to access a member (property or method) of a variable that is currently `null` (or `nullptr` in C++). This usually happens when a node hasn't been properly initialized or a reference to a node is lost. To fix it, ensure that all nodes are properly instantiated and assigned to variables before attempting to use them. Check for null values before accessing node properties.