Cloud Foundry Error – Failed to create default route from app name

Error:

$ cf push app/
Pushing app app/ to org sujeeth-org / space sujeeth-space as admin...
For application 'app/': Failed to create default route from app name: Host must be either "*" or contain only alphanumeric characters, "_", or "-"
FAILED

Solution:

Go inside a directory and run a command

$ cd app/


$ cf push