DefaultIfEmpty(TSource) Method (ParallelQuery(TSource), TSource)
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ParallelEnumerable.DefaultIfEmpty<'TSource> Method (ParallelQuery<'TSource>, 'TSource)

.NET Framework (current version)

Returns the elements of the specified parallel sequence or the specified value in a singleton collection if the sequence is empty.

Namespace:   System.Linq
Assembly:  System.Core (in System.Core.dll)

static member DefaultIfEmpty<'TSource> : 
        source:ParallelQuery<'TSource> *
        defaultValue:'TSource -> ParallelQuery<'TSource>


Type: System.Linq.ParallelQuery<'TSource>

The sequence to return the specified value for if it is empty.

Type: TSource

The value to return if the sequence is empty.

Return Value

Type: System.Linq.ParallelQuery<'TSource>

A sequence that contains defaultValue if source is empty; otherwise, source.

Type Parameters


The type of the elements of source.

Exception Condition

source is a null reference (Nothing in Visual Basic).


The query was canceled with the token passed in through WithCancellation.


One or more exceptions occurred during the evaluation of the query.

Universal Windows Platform
Available since 8
.NET Framework
Available since 4.0
Portable Class Library
Supported in: portable .NET platforms
Windows Phone
Available since 8.1
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