Call to UserAccessor.addUser() can result in IllegalArgumentException

2015-11-25 11:49:06,224 ERROR [http-nio-8081-exec-106] [lasso.migration.jersey.MigrationResource] createUser An error occured attempting to create a user
 -- url: /rest/lasso/1.0/migration/user | userName: lasso-admin
java.lang.IllegalArgumentException: User should not be null
	at com.atlassian.user.util.Assert.fail(Assert.java:12)
	at com.atlassian.user.util.Assert.notNull(Assert.java:25)
	at com.atlassian.crowd.embedded.atlassianuser.EmbeddedCrowdGroupManager.getCrowdUser(EmbeddedCrowdGroupManager.java:229)
	at com.atlassian.crowd.embedded.atlassianuser.EmbeddedCrowdGroupManager.addMembership(EmbeddedCrowdGroupManager.java:174)
	at sun.reflect.GeneratedMethodAccessor2234.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:497)
	at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:307)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:182)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:149)
	at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:106)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
	at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:204)
	at com.sun.proxy.$Proxy73.addMembership(Unknown Source)
	at bucket.user.DefaultUserAccessor.addUser(DefaultUserAccessor.java:76)
	at sun.reflect.GeneratedMethodAccessor1972.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:497)
	at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:307)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:182)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:149)
	at com.atlassian.spring.interceptors.SpringProfilingInterceptor.invoke(SpringProfilingInterceptor.java:16)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
	at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:106)
	at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
	at org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:204)