To reproduce just grab karaf 4 distro here:

install odl-restconf feature:

feature:install odl-restconf

install a second time:

feature:install odl-restconf

Now you get the following:

2017-05-03 11:09:10,281 | ERROR | nfig-blank-txn-0 | ConfigTransactionControllerImpl | 183 - org.opendaylight.controller.config-manager - 0.6.0.SNAPSHOT | Commit failed on ModuleIdentifier

{factoryName='rest-connector-impl', instanceName='rest-connector-default-impl'} in transaction TransactionIdentifier{name='ConfigTransaction-46-47'}
java.lang.NullPointerException
at org.osgi.util.tracker.ServiceTracker.<init>(ServiceTracker.java:184)[org.osgi.core-6.0.0.jar:]
at org.osgi.util.tracker.ServiceTracker.<init>(ServiceTracker.java:247)[org.osgi.core-6.0.0.jar:]
at org.opendaylight.controller.config.api.osgi.WaitingServiceTracker.create(WaitingServiceTracker.java:67)
at org.opendaylight.controller.config.yang.md.sal.rest.connector.RestConnectorModule.createInstance(RestConnectorModule.java:40)
at org.opendaylight.controller.config.spi.AbstractModule.getInstance(AbstractModule.java:87)
at sun.reflect.GeneratedMethodAccessor53.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)[:1.8.0_91]
at java.lang.reflect.Method.invoke(Method.java:498)[:1.8.0_91]
at org.opendaylight.controller.config.manager.impl.dependencyresolver.DependencyResolverManager$ModuleInvocationHandler.handleInvocation(DependencyResolverManager.java:148)
at com.google.common.reflect.AbstractInvocationHandler.invoke(AbstractInvocationHandler.java:87)
at com.sun.proxy.$Proxy89.getInstance(Unknown Source)
at org.opendaylight.controller.config.manager.impl.ConfigTransactionControllerImpl.secondPhaseCommit(ConfigTransactionControllerImpl.java:439)[183:org.opendaylight.controller.config-manager:0.6.0.SNAPSHOT]
at org.opendaylight.controller.config.manager.impl.ConfigRegistryImpl.secondPhaseCommit(ConfigRegistryImpl.java:347)[183:org.opendaylight.controller.config-manager:0.6.0.SNAPSHOT]
at org.opendaylight.controller.config.manager.impl.ConfigRegistryImpl.commitConfigSafe(ConfigRegistryImpl.java:288)[183:org.opendaylight.controller.config-manager:0.6.0.SNAPSHOT]
at org.opendaylight.controller.config.manager.impl.ConfigRegistryImpl.commitConfig(ConfigRegistryImpl.java:253)[183:org.opendaylight.controller.config-manager:0.6.0.SNAPSHOT]
at org.opendaylight.controller.config.manager.impl.osgi.BlankTransactionServiceTracker.lambda$new$0(BlankTransactionServiceTracker.java:42)[183:org.opendaylight.controller.config-manager:0.6.0.SNAPSHOT]
at org.opendaylight.controller.config.manager.impl.osgi.BlankTransactionServiceTracker.blankTransactionSync(BlankTransactionServiceTracker.java:75)[183:org.opendaylight.controller.config-manager:0.6.0.SNAPSHOT]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)[:1.8.0_91]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)[:1.8.0_91]
at java.lang.Thread.run(Thread.java:745)[:1.8.0_91]
2017-05-03 11:09:10,307 | ERROR | nfig-blank-txn-0 | ConfigRegistryImpl | 183 - org.opendaylight.controller.config-manager - 0.6.0.SNAPSHOT | Configuration Transaction failed on 2PC, server is unhealthy
java.lang.IllegalStateException: Error - getInstance() failed for ModuleIdentifier{factoryName='rest-connector-impl', instanceName='rest-connector-default-impl'}

in transaction TransactionIdentifier

{name='ConfigTransaction-46-47'}

at org.opendaylight.controller.config.manager.impl.ConfigTransactionControllerImpl.secondPhaseCommit(ConfigTransactionControllerImpl.java:446)[183:org.opendaylight.controller.config-manager:0.6.0.SNAPSHOT]
at org.opendaylight.controller.config.manager.impl.ConfigRegistryImpl.secondPhaseCommit(ConfigRegistryImpl.java:347)[183:org.opendaylight.controller.config-manager:0.6.0.SNAPSHOT]
at org.opendaylight.controller.config.manager.impl.ConfigRegistryImpl.commitConfigSafe(ConfigRegistryImpl.java:288)[183:org.opendaylight.controller.config-manager:0.6.0.SNAPSHOT]
at org.opendaylight.controller.config.manager.impl.ConfigRegistryImpl.commitConfig(ConfigRegistryImpl.java:253)[183:org.opendaylight.controller.config-manager:0.6.0.SNAPSHOT]
at org.opendaylight.controller.config.manager.impl.osgi.BlankTransactionServiceTracker.lambda$new$0(BlankTransactionServiceTracker.java:42)[183:org.opendaylight.controller.config-manager:0.6.0.SNAPSHOT]
at org.opendaylight.controller.config.manager.impl.osgi.BlankTransactionServiceTracker.blankTransactionSync(BlankTransactionServiceTracker.java:75)[183:org.opendaylight.controller.config-manager:0.6.0.SNAPSHOT]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)[:1.8.0_91]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)[:1.8.0_91]
at java.lang.Thread.run(Thread.java:745)[:1.8.0_91]
Caused by: java.lang.NullPointerException
at org.osgi.util.tracker.ServiceTracker.<init>(ServiceTracker.java:184)[org.osgi.core-6.0.0.jar:]
at org.osgi.util.tracker.ServiceTracker.<init>(ServiceTracker.java:247)[org.osgi.core-6.0.0.jar:]
at org.opendaylight.controller.config.api.osgi.WaitingServiceTracker.create(WaitingServiceTracker.java:67)
at org.opendaylight.controller.config.yang.md.sal.rest.connector.RestConnectorModule.createInstance(RestConnectorModule.java:40)
at org.opendaylight.controller.config.spi.AbstractModule.getInstance(AbstractModule.java:87)
at sun.reflect.GeneratedMethodAccessor53.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)[:1.8.0_91]
at java.lang.reflect.Method.invoke(Method.java:498)[:1.8.0_91]
at org.opendaylight.controller.config.manager.impl.dependencyresolver.DependencyResolverManager$ModuleInvocationHandler.handleInvocation(DependencyResolverManager.java:148)
at com.google.common.reflect.AbstractInvocationHandler.invoke(AbstractInvocationHandler.java:87)
at com.sun.proxy.$Proxy89.getInstance(Unknown Source)
at org.opendaylight.controller.config.manager.impl.ConfigTransactionControllerImpl.secondPhaseCommit(ConfigTransactionControllerImpl.java:439)[183:org.opendaylight.controller.config-manager:0.6.0.SNAPSHOT]
... 8 more
2017-05-03 11:09:10,376 | ERROR | nfig-blank-txn-1 | ConfigTransactionControllerImpl | 183 - org.opendaylight.controller.config-manager - 0.6.0.SNAPSHOT | Commit failed on ModuleIdentifier

{factoryName='rest-connector-impl', instanceName='rest-connector-default-impl'} in transaction TransactionIdentifier{name='ConfigTransaction-46-48'}
java.lang.NullPointerException
at org.osgi.util.tracker.ServiceTracker.<init>(ServiceTracker.java:184)[org.osgi.core-6.0.0.jar:]
at org.osgi.util.tracker.ServiceTracker.<init>(ServiceTracker.java:247)[org.osgi.core-6.0.0.jar:]
at org.opendaylight.controller.config.api.osgi.WaitingServiceTracker.create(WaitingServiceTracker.java:67)
at org.opendaylight.controller.config.yang.md.sal.rest.connector.RestConnectorModule.createInstance(RestConnectorModule.java:40)
at org.opendaylight.controller.config.spi.AbstractModule.getInstance(AbstractModule.java:87)
at sun.reflect.GeneratedMethodAccessor53.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)[:1.8.0_91]
at java.lang.reflect.Method.invoke(Method.java:498)[:1.8.0_91]
at org.opendaylight.controller.config.manager.impl.dependencyresolver.DependencyResolverManager$ModuleInvocationHandler.handleInvocation(DependencyResolverManager.java:148)
at com.google.common.reflect.AbstractInvocationHandler.invoke(AbstractInvocationHandler.java:87)
at com.sun.proxy.$Proxy89.getInstance(Unknown Source)
at org.opendaylight.controller.config.manager.impl.ConfigTransactionControllerImpl.secondPhaseCommit(ConfigTransactionControllerImpl.java:439)[183:org.opendaylight.controller.config-manager:0.6.0.SNAPSHOT]
at org.opendaylight.controller.config.manager.impl.ConfigRegistryImpl.secondPhaseCommit(ConfigRegistryImpl.java:347)[183:org.opendaylight.controller.config-manager:0.6.0.SNAPSHOT]
at org.opendaylight.controller.config.manager.impl.ConfigRegistryImpl.commitConfigSafe(ConfigRegistryImpl.java:288)[183:org.opendaylight.controller.config-manager:0.6.0.SNAPSHOT]
at org.opendaylight.controller.config.manager.impl.ConfigRegistryImpl.commitConfig(ConfigRegistryImpl.java:253)[183:org.opendaylight.controller.config-manager:0.6.0.SNAPSHOT]
at org.opendaylight.controller.config.manager.impl.osgi.BlankTransactionServiceTracker.lambda$new$0(BlankTransactionServiceTracker.java:42)[183:org.opendaylight.controller.config-manager:0.6.0.SNAPSHOT]
at org.opendaylight.controller.config.manager.impl.osgi.BlankTransactionServiceTracker.blankTransactionSync(BlankTransactionServiceTracker.java:75)[183:org.opendaylight.controller.config-manager:0.6.0.SNAPSHOT]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)[:1.8.0_91]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)[:1.8.0_91]
at java.lang.Thread.run(Thread.java:745)[:1.8.0_91]
2017-05-03 11:09:10,385 | ERROR | nfig-blank-txn-1 | ConfigRegistryImpl | 183 - org.opendaylight.controller.config-manager - 0.6.0.SNAPSHOT | Configuration Transaction failed on 2PC, server is unhealthy
java.lang.IllegalStateException: Error - getInstance() failed for ModuleIdentifier{factoryName='rest-connector-impl', instanceName='rest-connector-default-impl'}

in transaction TransactionIdentifier

{name='ConfigTransaction-46-48'}

at org.opendaylight.controller.config.manager.impl.ConfigTransactionControllerImpl.secondPhaseCommit(ConfigTransactionControllerImpl.java:446)[183:org.opendaylight.controller.config-manager:0.6.0.SNAPSHOT]
at org.opendaylight.controller.config.manager.impl.ConfigRegistryImpl.secondPhaseCommit(ConfigRegistryImpl.java:347)[183:org.opendaylight.controller.config-manager:0.6.0.SNAPSHOT]
at org.opendaylight.controller.config.manager.impl.ConfigRegistryImpl.commitConfigSafe(ConfigRegistryImpl.java:288)[183:org.opendaylight.controller.config-manager:0.6.0.SNAPSHOT]
at org.opendaylight.controller.config.manager.impl.ConfigRegistryImpl.commitConfig(ConfigRegistryImpl.java:253)[183:org.opendaylight.controller.config-manager:0.6.0.SNAPSHOT]
at org.opendaylight.controller.config.manager.impl.osgi.BlankTransactionServiceTracker.lambda$new$0(BlankTransactionServiceTracker.java:42)[183:org.opendaylight.controller.config-manager:0.6.0.SNAPSHOT]
at org.opendaylight.controller.config.manager.impl.osgi.BlankTransactionServiceTracker.blankTransactionSync(BlankTransactionServiceTracker.java:75)[183:org.opendaylight.controller.config-manager:0.6.0.SNAPSHOT]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)[:1.8.0_91]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)[:1.8.0_91]
at java.lang.Thread.run(Thread.java:745)[:1.8.0_91]
Caused by: java.lang.NullPointerException
at org.osgi.util.tracker.ServiceTracker.<init>(ServiceTracker.java:184)[org.osgi.core-6.0.0.jar:]
at org.osgi.util.tracker.ServiceTracker.<init>(ServiceTracker.java:247)[org.osgi.core-6.0.0.jar:]
at org.opendaylight.controller.config.api.osgi.WaitingServiceTracker.create(WaitingServiceTracker.java:67)
at org.opendaylight.controller.config.yang.md.sal.rest.connector.RestConnectorModule.createInstance(RestConnectorModule.java:40)
at org.opendaylight.controller.config.spi.AbstractModule.getInstance(AbstractModule.java:87)
at sun.reflect.GeneratedMethodAccessor53.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)[:1.8.0_91]
at java.lang.reflect.Method.invoke(Method.java:498)[:1.8.0_91]
at org.opendaylight.controller.config.manager.impl.dependencyresolver.DependencyResolverManager$ModuleInvocationHandler.handleInvocation(DependencyResolverManager.java:148)
at com.google.common.reflect.AbstractInvocationHandler.invoke(AbstractInvocationHandler.java:87)
at com.sun.proxy.$Proxy89.getInstance(Unknown Source)
at org.opendaylight.controller.config.manager.impl.ConfigTransactionControllerImpl.secondPhaseCommit(ConfigTransactionControllerImpl.java:439)[183:org.opendaylight.controller.config-manager:0.6.0.SNAPSHOT]
... 8 more