Returning null instead of an actual array, collection or map forces callers of the method to explicitly test for nullity, making them
more complex and less readable.
Moreover, in many cases, null is used as a synonym for empty.
Noncompliant code example
public static List<Result> getAllResults() {
return null; // Noncompliant
}
public static Result[] getResults() {
return null; // Noncompliant
}
public static Map<String, Object> getValues() {
return null; // Noncompliant
}
public static void main(String[] args) {
Result[] results = getResults();
if (results != null) { // Nullity test required to prevent NPE
for (Result result: results) {
/* ... */
}
}
List<Result> allResults = getAllResults();
if (allResults != null) { // Nullity test required to prevent NPE
for (Result result: allResults) {
/* ... */
}
}
Map<String, Object> values = getValues();
if (values != null) { // Nullity test required to prevent NPE
values.forEach((k, v) -> doSomething(k, v));
}
}
Compliant solution
public static List<Result> getAllResults() {
return Collections.emptyList(); // Compliant
}
public static Result[] getResults() {
return new Result[0]; // Compliant
}
public static Map<String, Object> getValues() {
return Collections.emptyMap(); // Compliant
}
public static void main(String[] args) {
for (Result result: getAllResults()) {
/* ... */
}
for (Result result: getResults()) {
/* ... */
}
getValues().forEach((k, v) -> doSomething(k, v));
}
