Object reference not set to an instance of an object

The “Object reference not set to an instance of an object” error in PowerShell means you tried to access a property or method on a variable that is $null.

What It Means

PowerShell is built on .NET, where every object reference either points to an actual instance or is $null. When you access a property ($obj.Property) or call a method ($obj.Method()) on a $null reference, .NET throws a NullReferenceException — the most common runtime exception across all .NET languages. The error tells you a reference was null but does not tell you which variable, so you must trace back through your code to find the source.

Why It Happens

• A cmdlet or function returned $null but you did not check the result.
• A hash key or array index does not exist: $data["missing"].
• A property on a nested object is null: $computer.BIOS.SerialNumber where $computer.BIOS is $null.
• You assigned $null earlier and forgot: $result = $null.
• An XML node or JSON field was not present in the parsed document.
• A parameter was not provided: param($Name) called without $Name.

How to Fix It

1. Check for null before accessing properties

# Bad
$process = Get-Process -Name "nonexistent" -ErrorAction SilentlyContinue
$process.Name

# Good
$process = Get-Process -Name "nonexistent" -ErrorAction SilentlyContinue
if ($process) {
    $process.Name
} else {
    Write-Warning "Process not found"
}

2. Use the null-conditional operator (PowerShell 7+)

# Only available in PowerShell 7 and later
$computer.BIOS?.SerialNumber

# Returns $null instead of throwing if BIOS is null

3. Use default values with the null-coalescing operator

# PowerShell 7+
$name = $user.Name ?? "Unknown"

# Or in older versions
$name = if ($user) { $user.Name } else { "Unknown" }

4. Check before method calls

$services = Get-Service -Name "Nonexistent" -ErrorAction SilentlyContinue
if ($null -ne $services) {
    $services.Start()
}

5. Verify hash tables and arrays have the key or index

$data = @{ name = "Alice" }

# Bad — key doesn't exist
$data.email.ToString()

# Good — check first
if ($data.ContainsKey("email")) {
    $data.email.ToString()
}

# Or use TryGetValue
$value = $null
if ($data.TryGetValue("email", [ref]$value)) {
    $value.ToString()
}

6. Trace null sources with verbose output

Write-Debug "Variable `$result is: $($result | Out-String)"
$result.Property   # If this fails, the debug output shows what $result was