Exception calling "ToUInt32" with "1" argument(s): "Input string was not in a correct format."

Running the preparesubnet.ps1 script results in the following error:

Selecting subscription 'REDACTED'.
Subscription selected.
Loading virtual network 'vnw-redacted-dev-az1-vnet' in resource group 'rsg-redacted-dev-az1-vnet'.
Virtual network loaded.
Loading subnet 'sbt-redacted-app'.
Subnet loaded.

Verifying subnet 'sbt-redacted-app'.
Passed Validation - Subnet is of enough size.
Passed Validation - There are no conflicting resources inside the subnet.
Verifying DNS servers list for virtual network 'vnw-redacted-dev-az1-vnet'.
Passed Validation - DNS Servers List.
Verifying Service endpoints for subnet 'sbt-redacted-app'.
Passed Validation - No service endpoints.
Verifying Network security group for subnet 'sbt-redacted-app'.
Loading Network security group for subnet 'sbt-redacted-app'.
Warning - Network security group needs modifications.
Verifying RT for subnet 'sbt-redacted-app'.
Loading Route table for subnet 'sbt-redacted-app'.
Route table loaded.
Verifying Route table 'rtb-redacted-dev-az1-app'.

Exception calling "ToUInt32" with "1" argument(s): "Input string was not in a correct format."
At /home/jenkins/workspace/module-tests/scripts/prepareSubnet.ps1:284 char:5
+     $ipnum = ([Convert]::ToUInt32($cidrRangeParts[0]) -shl 24) -bor `
+     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
+ FullyQualifiedErrorId : FormatException

Exception calling "ToUInt32" with "1" argument(s): "Input string was not in a correct format."
At /home/jenkins/workspace/module-tests/scripts/prepareSubnet.ps1:284 char:5
+     $ipnum = ([Convert]::ToUInt32($cidrRangeParts[0]) -shl 24) -bor `
+     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
+ FullyQualifiedErrorId : FormatException

Exception calling "ToUInt32" with "1" argument(s): "Input string was not in a correct format."
At /home/jenkins/workspace/module-tests/scripts/prepareSubnet.ps1:284 char:5
+     $ipnum = ([Convert]::ToUInt32($cidrRangeParts[0]) -shl 24) -bor `
+     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
+ FullyQualifiedErrorId : FormatException

Passed Validation - Route table.

Start in scripts/prepareSubnet.ps1 at line 284, where route table validation calls ToUInt32 while processing the route table. Reproduce the prepareSubnet.ps1 run through route table verification and inspect the CIDR parts used there. Done means route table validation completes without the FormatException.