== Why is this an issue?

Map https://docs.oracle.com/javase/8/docs/api/java/util/Map.html#computeIfAbsent-K-java.util.function.Function-[computeIfAbsent] and https://docs.oracle.com/javase/8/docs/api/java/util/Map.html#computeIfPresent-K-java.util.function.BiFunction-[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

[source,java]
----
map.computeIfAbsent(key, k -> null); // Noncompliant, the map will not contain an entry key->null.
map.computeIfPresent(key, (k, oldValue) -> null); // Noncompliant
----


=== Compliant solution

[source,java]
----
if (!map.containsKey(key)) {
    map.put(key, null);
}
if (map.containsKey(key)) {
    map.put(key, null);
}
----

== Resources

=== Related rules

* S3824 - "Map.get" and value test should be replaced with a single method call


ifdef::env-github,rspecator-view[]

'''
== Implementation Specification
(visible only on this page)

=== Message

Use "Map.containsKey(key)" followed by "Map.put(key, null)" to add null values.


=== Highlighting

* Primary: computeIfAbsent method name
* Secondary: null literal in the argument.

** Message: The entry will not be put into the Map.


'''
== Comments And Links
(visible only on this page)

=== relates to: S3824

endif::env-github,rspecator-view[]