I have an Oracle  12.1.0.2c cluster having following 5 nodes :

• Hub Nodes : host01, host02, host03
• Leaf nodes: host04 and host05

I wanted to install RAC database software on the 3 hub nodes i.e. host01, host02 and host03.

I invoked the OUI as oracle user (Owner of Database Home)

[oracle@host01 database_12_1_0_2]$ ./runInstaller

and chose the option to install RAC database software only on the 3 hub nodes.

After all the pre-requisite checks were successful , I clicked the Install button.
I got the error: java.lang nullpointerexception

On clicking OK, the OUI aborted.

To troubleshoot, I ran the OUI in debug mode as :

[oracle@host01 database_12_1_0_2]$ ./runInstaller -debug -J-DTRACING.ENABLED=true -J-DTRACING.LEVEL=2 -J-DSRVM_TRACE_LEVEL=2 -J-DFULLTRACE

The trace file showed that the leaf node host05 was not responding:

[setup.flowWorker] [ 2016-04-18 14:33:22.771 IST ]
[CRSCTLUtil.getClusterNodeConfigRoles:1198] outputs[4] = CRS-4404: The following nodes did not reply within the allotted time:
[setup.flowWorker] [ 2016-04-18 14:33:22.772 IST ]
[CRSCTLUtil.getClusterNodeConfigRoles:1200] values length = 2
[setup.flowWorker] [ 2016-04-18 14:33:22.772 IST ]
[CRSCTLUtil.getClusterNodeConfigRoles:1198] outputs[5] = host05
[setup.flowWorker] [ 2016-04-18 14:33:22.772 IST ]
[CRSCTLUtil.getClusterNodeConfigRoles:1200] values length = 1

I realized that although I wanted to install database software on 3 nodes only, all the nodes
needed to be up and running whereas in my case, the node host05 was down at that time.

When I started the node host05 and reinvoked OUI, the database software was installed
successfully.

References:
http://www.hhutzler.de/blog/oracle-installer-and-rac-installation/