while creating external network subnet range through Horizon UI helper message says give subnet range as comma separated but accept hyphen("-")

Description: When user is trying to create an external network with subnet range using hyphen "-" delimiter (20.x.x.10-20.x.x.100) even when the helper message says clearly notify user the "(start_ip_range,end_ip_range) as comma separated delimeter" is going through successfully without error message. please see the Ui attachment for more info.

Also after giving Hyphen range in the external subnet. External network window leads to an unexpected error saying "Specify additional attributes for the subnet" without giving any proper error message.

Pre - condition :
create a tenant router r1 router with gateway external network .

Step1 ->Create external network using admin user from Horizon.
Step2 ->on the create network window . name -> external
                                       project->admin
                                       provider network type->external
                                       leave the physical network blank(but make sure user has tier 0 gateway set)
Step3-> click next-> subnet name -> subnet1
                     network address-> Try to give external network range as that of the gateway ip.
                     Gateway IP-> Give the gateway IP of the subnet

Step4-> under subnet details. Uncheck the "Enable Dhcp".
                              allocation pool-> give subnet range as (20.x.x.10-20.x.x.100)

Step5-> Once user click "next" window comes back to step2 and further clicking next leads to message "Specify additional attributes for the subnet"