Map computeIfAbsent and computeIfPresent methods are
convenient to avoid the cumbersome process to check if a key exists or not, followed by the addition of the entry. However, when the function used to
compute the value returns null, the entry key->null will not be added to the Map. Furthermore, in the case of
computeIfPresent, if the key is present the entry will be removed. These methods should therefore not be used to conditionally add an
entry with a null value. The traditional way should be used instead.
This rule raises an issue when computeIfAbsent or computeIfPresent is used with a lambda always returning null.
Noncompliant code example
map.computeIfAbsent(key, k -> null); // Noncompliant, the map will not contain an entry key->null.
map.computeIfPresent(key, (k, oldValue) -> null); // Noncompliant
Compliant solution
if (!map.containsKey(key)) {
map.put(key, null);
}
if (map.containsKey(key)) {
map.put(key, null);
}
