Fix for NPE when Thread.currentThread().getContextClassLoader() is null.

[beccagaspard]

Fix for NPE in STGroup::getUrl when Thread.currentThread().getContextClassLoader() is null. We experienced this issue with version 4.0.8 in an OSGI environment where Thread.currentThread().getContextClassLoader() was null but this.getClass().getClassLoader() was populated and would have been able to resolve the fileName if a NPE had not been thrown. Added null check for both classloaders. I tried to follow your existing code formatting, please let me know if any changes are needed! 🤓

Stacktrace:

can't load group file jar:file:/usr/local/tomcat/webapps/ROOT/WEB-INF/lib/killbill-invoice-0.22.10.jar!/org/killbill/billing/invoice/dao/InvoiceSqlDao.sql.stg
Caused by: java.lang.NullPointerException
    at org.stringtemplate.v4.STGroup.getURL(STGroup.java:774)
    at org.stringtemplate.v4.STGroupFile.<init>(STGroupFile.java:67)
    at org.stringtemplate.v4.STGroup.importTemplates(STGroup.java:563)
    at org.stringtemplate.v4.compiler.GroupParser.group(GroupParser.java:199)
    at org.stringtemplate.v4.STGroup.loadGroupFile(STGroup.java:612)
    at org.stringtemplate.v4.STGroupFile.load(STGroupFile.java:139)
    at org.stringtemplate.v4.STGroupFile.load(STGroupFile.java:128)
    at org.skife.jdbi.v2.sqlobject.stringtemplate.ST4StatementLocator$STGroupFileWithThreadSafeLoading.lookupTemplate(ST4StatementLocator.java:343)
    at org.stringtemplate.v4.STGroup.getInstanceOf(STGroup.java:165)
    at org.skife.jdbi.v2.sqlobject.stringtemplate.ST4StatementLocator.locateAndRender(ST4StatementLocator.java:291)
    at org.skife.jdbi.v2.sqlobject.stringtemplate.ST4StatementLocator.locateFromCache(ST4StatementLocator.java:279)
    at org.skife.jdbi.v2.sqlobject.stringtemplate.ST4StatementLocator.locate(ST4StatementLocator.java:242)
    at org.skife.jdbi.v2.SQLStatement.wrapLookup(SQLStatement.java:1288)
    at org.skife.jdbi.v2.SQLStatement.internalExecute(SQLStatement.java:1297)
    at org.skife.jdbi.v2.Query.fold(Query.java:173)
    at org.skife.jdbi.v2.Query.first(Query.java:275)
    at org.skife.jdbi.v2.Query.first(Query.java:264)
    at org.skife.jdbi.v2.sqlobject.ResultReturnThing$SingleValueResultReturnThing.result(ResultReturnThing.java:112)
    at org.skife.jdbi.v2.sqlobject.ResultReturnThing.map(ResultReturnThing.java:48)
    at org.skife.jdbi.v2.sqlobject.QueryHandler.invoke(QueryHandler.java:45)
    at org.skife.jdbi.v2.sqlobject.SqlObject.invoke(SqlObject.java:180)
    at org.skife.jdbi.v2.sqlobject.SqlObject$1.intercept(SqlObject.java:76)
    at org.skife.jdbi.v2.sqlobject.CloseInternalDoNotUseThisClass$$EnhancerByCGLIB$$fa65c70f.getById(<generated>)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    ...

[parrt]

thanks very much @beccagaspard !