In Beryllium CSIT, there is a test case which sends data [0].
This data does not contain keepalive-executor container. The container would have "type" field, which is explicitly set as not mandatory in [1], but it would also have a "name" field, which is inherited as mandatory from [2].

ODL resolves this situation as user error, as "name" is mandatory but not present in data.
This is possibly a netconf Bug, odl-sal-netconf-connector-cfg.yang should make sure keepalive-executor is not mandatory.

Looking at [3], this can be fixed by making keepalive-executor a presence container, in which case "type" may be kept mandatory.

Here is a piece of karaf.log:

Caused by: java.lang.IllegalArgumentException: Node (urn:opendaylight:params:xml:ns:yang:controller:config?revision=2013-04-05)configuration is missing mandatory descendant /(urn:opendaylight:params:xml:ns:yang:controller:md:sal:connector:netconf?revision=2015-08-03)keepalive-executor/name
at com.google.common.base.Preconditions.checkArgument(Preconditions.java:145)[39:com.google.guava:18.0.0]
at org.opendaylight.yangtools.yang.data.impl.schema.tree.MandatoryLeafEnforcer$Strict.enforceOnTreeNode(MandatoryLeafEnforcer.java:58)[59:org.opendaylight.yangtools.yang-data-impl:0.8.0.SNAPSHOT]

[0] https://jenkins.opendaylight.org/releng/view/netconf/job/netconf-csit-1node-userfeatures-only-beryllium/lastSuccessfulBuild/robot/report/log.html#s1-s2-s1-t36-k2-k1-k2-k1-k3
[1] https://git.opendaylight.org/gerrit/gitweb?p=netconf.git;a=blob;f=opendaylight/netconf/sal-netconf-connector/src/main/yang/odl-sal-netconf-connector-cfg.yang;h=d903ccfa248f0a0409d2ae20c1a57b76fdf9ed49;hb=db7649383aa96be597a77f7a6da2b40be6fefc22#l171
[2] https://git.opendaylight.org/gerrit/gitweb?p=controller.git;a=blob;f=opendaylight/config/config-api/src/main/yang/config.yang;h=e46d327ece9aff4e89ecf7ab0088561acb17c5aa;hb=37cbf86dd56fb1d79a817750951283e1ae688cf7#l131
[3] http://tools.ietf.org/html/rfc6020#section-7.6.5