Empty string in resource name fails, even when the resourse will not be used.

[chambersDon]

Bicep version
Bicep CLI version 0.31.92 (b065093)

Describe the bug
Optional parameters that default to empty string cause the error below, even though an if condition would cause the resource not to be used:
The template reference 'existingSubnet' is not valid: could not find template resource or resource copy with this name

To Reproduce
run this bicep:

param location string = 'CentralUS'
param resourceGroupForVnet string = ''
param vnetName string = ''
param subnetName string = ''
param allowPublicAccess bool = true


var blobPrivateEndpointName = 'pe-testendpoint'


resource existingSubnet 'Microsoft.Network/virtualNetworks/subnets@2022-05-01' existing = if(!allowPublicAccess) {
  name: '${vnetName}/${subnetName}'
  scope: resourceGroup(resourceGroupForVnet)
}

resource thePE 'Microsoft.Network/privateEndpoints@2022-11-01' = if(!allowPublicAccess){
  name: blobPrivateEndpointName
  location: location
  properties: {
    subnet: {
      id: existingSubnet.id
    }
  }
}


type grantType = {}

---

With version 0.31.92 you will get this error:

Additional context
I was getting this error when uses version 0.29.45. I upgraded to 0.31.34 and the error went away. Last week, I upgraded to 0.31.92 and the error has returned.

If I remove the thePE resource OR the type defintion then I don't get the error.

[jeskew]

@chambersDon The fix in 0.31.34 had to be reverted but should be back for v0.32. There's some more context in the description of #15580 if you're curious.