Invalid namespace URI with nullpointer exception occurred when namspace contains underscore

Yang :
module moduletest {
yang-version 1;
namespace "onos_yang_1:level1:newlevel";
prefix test;

organization "huawei";
contact "adarsh.m@huawei.com";
description "test";

revision 2015-10-12;
leaf leaf2-to

}

Logs :

INFO] — yangutils-maven-plugin:1.0.0-SNAPSHOT:yang2java (default) @ onlab-test —
[INFO] Error in file: /opt/onos-master/onos/utils/test/src/main/yang/Onos_Yang_1.yang at line: 3 at position: 14
YANG file error: Invalid namespace URI
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 1.842 s
[INFO] Finished at: 2016-05-12T18:45:56+05:30
[INFO] Final Memory: 18M/306M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.onosproject:yangutils-maven-plugin:1.0.0-SNAPSHOT:yang2java (default) on project onlab-test: Execution default of goal org.onosproject:yangutils-maven-plugin:1.0.0-SNAPSHOT:yang2java failed. NullPointerException -> [Help 1]
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/PluginExecutionException
root1@root1-HP-EliteBook-840-G2:/opt/onos-master/onos/utils/test$