Question:
In PowerShell one can define C# code and execute it. Passing in $null into the following simplest function shows that not null gets passed into the function
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Add-Type -TypeDefinition @" public static class foo { public static void fooo(string a) { if(a!=null) { System.Console.WriteLine("Not Null. Is '" + a + "'"); } } } "@ -Language CSharp |
Calling it as follows leads to the output Not Null. Is ”. This shows that $null was not null in C#. Methods like ‘IsNullOrEmpty’ or ‘IsNullOrWhiteSpace’ return true, so PowerShell must have implicitly converted the $null into a string.
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[foo]::fooo($Null) |
Any ideas why this is happening and if there is a better fix apart from rather calling String.IsNullOrEnpty in C#?
NB: This happens irrespective of the C# language specified ‘Add_Type’. I’m using PowerShell V5.
Answer:
Evidently the solution is “don’t pass $null to a [String] parameter if you want a $null [String]“. There is a special [NullString] class that should be used instead.
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PS > [foo]::fooo($Null) Not Null. Is '' PS > [foo]::fooo([NullString]::Value) PS > |
I can’t find any mentions of the need to use [NullString] in the PowerShell documentation, nor does the source code for the NullString class include any comments explaining its purpose.