== Why is this an issue?

Returning ``++null++`` or ``++default++`` instead of an actual collection forces the method callers to explicitly test for null, making the code more complex and less readable.

Moreover, in many cases, ``++null++`` or ``++default++`` is used as a synonym for empty.


=== Noncompliant code example

[source,csharp]
----
public Result[] GetResults()
{
    return null; // Noncompliant
}

public IEnumerable<Result> GetResults(bool condition)
{
    var results = GenerateResults();
    return condition 
        ? results 
        : null; // Noncompliant
}

public IEnumerable<Result> GetResults() => null; // Noncompliant

public IEnumerable<Result> Results 
{
    get
    {
        return default(IEnumerable<Result>); // Noncompliant
    }
}

public IEnumerable<Result> Results => default; // Noncompliant
----

=== Compliant solution

[source,csharp]
----
public Result[] GetResults()
{
    return new Result[0];
}

public IEnumerable<Result> GetResults(bool condition)
{
    var results = GenerateResults();
    return condition 
        ? results 
        : Enumerable.Empty<Result>(); 
}

public IEnumerable<Result> GetResults() => Enumerable.Empty<Result>();

public IEnumerable<Result> Results 
{
    get
    {
        return Enumerable.Empty<Result>();
    }
}

public IEnumerable<Result> Results => Enumerable.Empty<Result>();
----

=== Exceptions

Although ``++string++`` is a collection, the rule won't report on it.


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

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

include::../message.adoc[]

'''
== Comments And Links
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include::../comments-and-links.adoc[]

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