Let’s assume in an array you want to get rid of all elements that are either empty or null. This is what many would do:

 
PS> 1,2,$null,"test","",9 | Where-Object { $_ -ne '' -and $_ -ne $null }

1
2
test
9

PS>  
 

However, this comparison is dangerous because it also eliminates the value 0:

 
PS> 1,2,0,$null,"test","",0,9 | Where-Object { $_ -ne '' -and $_ -ne $null }

1
2
test
9

PS>  
 

PowerShell filters out the value 0 because it equals to an empty string:

 
PS> 0 -eq ''
True

PS> 1 -eq ''
False
 

This is because with comparisons, the data type of the left side counts, and since there is an integer on the left side, PowerShell converts the empty string to an integer as well, which happens to be the value 0.

In order to do a safe comparison, always make sure you place the relevant data type on the left side, not the right:

 
PS> 1,2,0,$null,"test","",0,9 | Where-Object { '' -ne $_ -and $null -ne $_ }

1
2
0
test
0
9

PS> 
 

Or better yet, use one of the API functions to identify empty values:

 
PS> 1,2,0,$null,"test","",0,9 | Where-Object { ![string]::IsNullOrWhiteSpace($_) }

1
2
0
test
0
9

PS>  
 

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