Deal with empty (and `$Null`) inputs

[iRon7]

Considered how to deal with $Null and empty array inputs:

• @() |Join $Object
  This situation could potentially occur from a chained (inner) join.
  But at the other hand, could useful as initial "object" in an loop: ... |% { $a = $Null } { $a = $a |Join $_ }
• $Object |Join $Null or $Object |Join @()

Current situation:

PS C:\> $Null |Join $Employee |Ft

Id     Name               Country            Department                 Age      ReportsTo
--     ----               -------            ----------                 ---      ---------
{1, 1} {Aerts, Aerts}     {Belgium, Belgium} {Sales, Sales}             {40, 40} {5, 5}
{2, 2} {Bauer, Bauer}     {Germany, Germany} {Engineering, Engineering} {31, 31} {4, 4}
{3, 3} {Cook, Cook}       {England, England} {Sales, Sales}             {69, 69} {1, 1}
{4, 4} {Duval, Duval}     {France, France}   {Engineering, Engineering} {21, 21} {5, 5}
{5, 5} {Evans, Evans}     {England, England} {Marketing, Marketing}     {35, 35} {, }
{6, 6} {Fischer, Fischer} {Germany, Germany} {Engineering, Engineering} {29, 29} {4, 4}

PS C:\> @() |Join $Employee |Ft

Id     Name               Country            Department                 Age      ReportsTo
--     ----               -------            ----------                 ---      ---------
{1, 1} {Aerts, Aerts}     {Belgium, Belgium} {Sales, Sales}             {40, 40} {5, 5}
{2, 2} {Bauer, Bauer}     {Germany, Germany} {Engineering, Engineering} {31, 31} {4, 4}
{3, 3} {Cook, Cook}       {England, England} {Sales, Sales}             {69, 69} {1, 1}
{4, 4} {Duval, Duval}     {France, France}   {Engineering, Engineering} {21, 21} {5, 5}
{5, 5} {Evans, Evans}     {England, England} {Marketing, Marketing}     {35, 35} {, }
{6, 6} {Fischer, Fischer} {Germany, Germany} {Engineering, Engineering} {29, 29} {4, 4}

PS C:\> $Employee |Join $Null |Ft
InvalidOperation: C:\Join.ps1:345
Line |
 345 |  … in $Keys) { $Properties.Add($Key, $Object.psobject.properties[$Key].V …
     |                ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     | Cannot index into a null array.


Id Name  Country Department Age ReportsTo
-- ----  ------- ---------- --- ---------
 1 Aerts Belgium Sales       40         5

PS C:\> $Employee |Join @() |Ft
InvalidOperation: C:\Join.ps1:454
Line |
 454 |                  ([ref]$RightKeys).Value = $Right.get_Keys()
     |                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     | You cannot call a method on a null-valued expression.

MethodInvocationException: C:\Join.ps1:371
Line |
 371 |                      if (!$Expressions.Contains($Key)) {
     |                          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     | Exception calling "Contains" with "1" argument(s): "Value cannot be null. (Parameter 'key')"

[iRon7]

This doesn't return anything because there is no relation between the id's:

@{id = 1; name = 'one'} |Join @{id = 2; name = 'Two'} -On id

Expected:

Therefore it is expected that chaining it to a third object should still return nothing:

@{id = 1; name = 'one'} |Join @{id = 2; name = 'Two'} -On id |Join @{id = 3; name = 'Three'} -On id

Actual

But instead is does a self-join on the last object and returns:

name           id
----           --
{Three, Three}  3

[iRon7]

Fixed in version 3.4.6

@() |Join $Employee | Should -benull

$Actual = $Employee |Join $Null 
$Expected = [PSCustomObject]@{Id = 1; Name = 'Aerts'; Country = 'Belgium'; Department = 'Sales'; Age = 40; ReportsTo = 5}
Compare-PSObject $Actual $Expected | Should -BeNull

$Employee |Join @() | Should -benull

@{id = 1; name = 'one'} |Join @{id = 2; name = 'Two'} -On id | Should -benull

@{id = 1; name = 'one'} |Join @{id = 2; name = 'Two'} -On id |Join @{id = 3; name = 'Three'} -On id | Should -benull

@() |Join @{id = 3; name = 'Three'} -On id | Should -benull

$Actual = Join @{id = 3; name = 'Three'} -On id
$Expected = [PSCustomObject]@{name = [array]('Three', 'Three'); id = 3}
Compare-PSObject $Actual $Expected | Should -BeNull

[iRon7]

Version 3.8 (prerelease), joining with $Null doesn't return anything

$Employee |Join $Null | Should -benull