Void safety is a static (compile-time) guarantee that no object references will have null or void values.
Access to objects is achieved through references (or, equivalently, pointers). A typical call is of the form:
```
x.f(a, ...)
```
where f denotes an operation and x denotes a reference to some object. At execution time, however, a reference can be void (or null). In such cases, the call above will be a void call, leading to a run-time exception, often resulting in abnormal termination of the program.