Handling null values in logical expressions

If your data can provide null values, you need to be aware of how Gosu handles these values in logical expressions. Using the null-safe operators can propagate null values from their original sources into other objects and variables in your code.

In an equality test, Gosu returns true if both sides of the operator are null and false otherwise.
In a Boolean expression that uses the and, or, or not operators, Gosu treats null as a value of false.

Be particularly aware of the possibility of null values in code that uses the and, or, or not operators. If you use null-safe method operators in logical expressions, your code can produce unexpected results:

var nullStr : String // A string that contains the null value 

// Test whether the string is empty 
if (nullStr?.isEmpty()) {
  print("Empty string") // This message does not appear even though there is nothing in the string.
  // Code here to put a value into an empty string does not execute for the null string.
}
// Test whether the string is not empty 
if (!nullStr?.isEmpty()) {
  print("Got here!") // This message does appear, but the string has no contents.
  // If you put code here to use the string value, you risk a null-pointer exception.
}