This is identical to the message posted on April 3 by Ameen Ali.
After a fresh installation on ubuntu 16.04 the only inputs available are Beats, 3 AWS Inputs (Flow, Logs, and CloudTrail, and 2 CEF Inputs (AMQP & Kafka).
His solution was refreshing the browser.
When I executed the suggested curl command:
curl -H ‘Accept: application/json’ ‘http://MYSERVER.COM:9000/api/system/inputs/types?pretty=true’
The output was null.
Flushing my browser cache or connecting with a different browser returned the same list of inputs.