A null key is not allowed in a hash literal - powershell

Question

I would like to be able to save this hashtable in a variable called: $arr.
As you can see we define two variables $displayName and $typekind and I put them in the hashtable.
But when i try to run the script it gives me an error:
InvalidOperation: A null key is not allowed in a hash literal.
I have tried some different things but i am not sure where error is happening. Hope you can help me
...
if (!( $resourceTypes -like ("*" + $resource.type + "*")) -and ($azDiagSetting)) {
$displayName = $resource.type.replace('/', ' ').Split(' ')[-1]
$typekind = $resource.type
$arr = #{
type = "Microsoft.Authorization/policyDefinitions"
apiVersion = "2020-09-01"
properties = #{
metadata = #{
category = "Monitoring"
}
description = "This policy automatically deploys and enable diagnostic settings to Log Analytics"
displayName = "Apply diagnostic settings for $($displayName) - Log Analytics"
policyRule = #{
then = #{
details = #{
roleDefinitionIds = #(
"/providers/Microsoft.Authorization/roleDefinitions/92aaf0da-9dab-42b6-94a3-d43ce8d16293"
)
name = "setByPolicy"
type = "Microsoft.Insights/diagnosticSettings"
existenceCondition = #{
AllOf = #(
#{
matchInsensitively = "[[parameters('logAnalytics')]"
field = "Microsoft.Insights/diagnosticSettings/workspaceId"
}
)
}
deployment = #{
properties = #{
template = #{
contentVersion = "1.0.0.0"
resources = #(
#{
type = "$($typekind)/providers/diagnosticSettings"
apiVersion = "2021-05-01-preview"
properties = #{
metrics = #(
#{ }
)
workspaceId = "[[parameters('logAnalytics')]"
logs = #(
#{}
)
}
location = "[[parameters('location')]"
name = "[[concat(parameters('resourceName'), '/', 'Microsoft.Insights/setByPolicy')]"
}
)
parameters = #{
location = #{
type = "string"
}
logAnalytics = #{
type = "string"
}
resourceName = #{
type = "string"
}
}
$schema = "http://schema.management.azure.com/schemas/2015-01-01/deploymentTemplate.json#"
}
parameters = #{
location = #{
value = "[[field('location')]"
}
logAnalytics = #{
value = "[[parameters('logAnalytics')]"
}
resourceName = #{
value = "[[field('name')]"
}
}
mode = "incremental"
}
}
}
}
}
}
} | ConvertTo-Json -Depth 20
$arr
}

Answer 1

PowerShell is attempting to assign the value of $schema (a variable) as a Key of your hash table. As it seems and could be the only possible explanation for your error, this variable hasn't been defined hence is effectively $null:
$schema = $null
$hash = #{
$schema = 'hello'
}
# Above errors with the exception message:
# "A null key is not allowed in a hash literal."
If you want to assign $schema as the literal name of your Key, you can use single-quoted strings:
A string enclosed in single-quotation marks is a verbatim string. The string is passed to the command exactly as you type it. No substitution is performed.
$hash = #{
'$schema' = 'hello'
}
# Results in:
Name Value
---- -----
$schema hello