Bicep diagnostic code - BCP401

This diagnostic occurs when you use expressions to define resource bodies as the Spread operator gets converted to a function. It's a limitation in JSON.

The spread operator "..." is not permitted in this location.

Error

The following example raises the diagnostic because the spread operator is used to define the resource body:

param location string = resourceGroup().location
param addressPrefix string = '10.0.0.0/24'
 
resource vnet 'Microsoft.Network/virtualNetworks@2024-01-01' = {
  name: 'vnetName'
  location: location
 
  ...(addressPrefix != '' ? {
    properties: {
      addressSpace: {
        addressPrefixes: [
          addressPrefix
        ]
      }
    }
  } : {})
}

You can fix the diagnostic by using the operator in the lower level:

param location string = resourceGroup().location
param addressPrefix string = '10.0.0.0/24'
 
resource vnet 'Microsoft.Network/virtualNetworks@2024-01-01' = {
  name: 'vnetName'
  location: location
 
  properties: {
    addressSpace: {
      ...(addressPrefix != '' ? {
        addressPrefixes: [
          addressPrefix
        ]        
      } : {})
    }
  }
}

For more information about Bicep diagnostics, see Bicep core diagnostics.