Parser: Only the last prefix works if the module is imported multiple times

First of all, importing from the same module with different prefixes may be violating the Yang standard, although the relevant sentence is not very explicit:

Multiple "import" statements may be specified to import from different modules.
https://tools.ietf.org/html/rfc6020#section-7.1.5

Anyway, current ODL behavior differs on which prefix is then used. Here are simple test models: https://git.opendaylight.org/gerrit/#/c/41269/1

Ideally, parser could support multiple prefixes pointing to the same imported model.
If that is not easy to implement, parser should at least produce an Exception with a message informing about multiple import from the same module.

Currently the exception only informs about not finding the desired node:

[ERROR] yang-to-sources: Unable to parse yang files from /home/odl/build/mdsal/model/test/bug-augment/src/main/yang
java.lang.IllegalArgumentException: Failed to parse node 'bt0:target' in path '/bt0:target'
at org.opendaylight.yangtools.yang.parser.stmt.rfc6020.Utils.nodeIdentifierFromPath(Utils.java:452)
at org.opendaylight.yangtools.yang.parser.stmt.rfc6020.AugmentStatementImpl$Definition.parseArgumentValue(AugmentStatementImpl.java:75)
at org.opendaylight.yangtools.yang.parser.stmt.rfc6020.AugmentStatementImpl$Definition.parseArgumentValue(AugmentStatementImpl.java:62)
at org.opendaylight.yangtools.yang.parser.stmt.reactor.StatementDefinitionContext.parseArgumentValue(StatementDefinitionContext.java:34)
at org.opendaylight.yangtools.yang.parser.stmt.reactor.SubstatementContext.<init>(SubstatementContext.java:47)
at org.opendaylight.yangtools.yang.parser.stmt.reactor.StatementContextBase$1.build(StatementContextBase.java:327)
at org.opendaylight.yangtools.yang.parser.stmt.reactor.StatementContextWriter.defferedCreate(StatementContextWriter.java:45)
at org.opendaylight.yangtools.yang.parser.stmt.reactor.StatementContextWriter.startStatement(StatementContextWriter.java:32)
at org.opendaylight.yangtools.yang.parser.impl.YangStatementParserListenerImpl.enterStatement(YangStatementParserListenerImpl.java:82)
at org.opendaylight.yangtools.antlrv4.code.gen.YangStatementParser$StatementContext.enterRule(YangStatementParser.java:113)
at org.antlr.v4.runtime.tree.ParseTreeWalker.enterRule(ParseTreeWalker.java:66)
at org.antlr.v4.runtime.tree.ParseTreeWalker.walk(ParseTreeWalker.java:49)
at org.antlr.v4.runtime.tree.ParseTreeWalker.walk(ParseTreeWalker.java:52)
at org.antlr.v4.runtime.tree.ParseTreeWalker.walk(ParseTreeWalker.java:52)
at org.opendaylight.yangtools.yang.parser.stmt.rfc6020.YangStatementSourceImpl.writeFull(YangStatementSourceImpl.java:98)
at org.opendaylight.yangtools.yang.parser.stmt.reactor.SourceSpecificContext.loadStatements(SourceSpecificContext.java:329)
at org.opendaylight.yangtools.yang.parser.stmt.reactor.BuildGlobalContext.loadPhaseStatements(BuildGlobalContext.java:228)
at org.opendaylight.yangtools.yang.parser.stmt.reactor.BuildGlobalContext.buildEffective(BuildGlobalContext.java:196)
at org.opendaylight.yangtools.yang.parser.stmt.reactor.CrossSourceStatementReactor$BuildAction.buildEffective(CrossSourceStatementReactor.java:134)
at org.opendaylight.yangtools.yang.parser.stmt.reactor.CrossSourceStatementReactor$BuildAction.buildEffective(CrossSourceStatementReactor.java:151)
at org.opendaylight.yangtools.yang2sources.plugin.YangToSourcesProcessor.processYang(YangToSourcesProcessor.java:177)
at org.opendaylight.yangtools.yang2sources.plugin.YangToSourcesProcessor.execute(YangToSourcesProcessor.java:93)
at org.opendaylight.yangtools.yang2sources.plugin.YangToSourcesProcessor.conditionalExecute(YangToSourcesProcessor.java:104)
at org.opendaylight.yangtools.yang2sources.plugin.YangToSourcesMojo.execute(YangToSourcesMojo.java:119)
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:134)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:207)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:153)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:145)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:116)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:80)
at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build(SingleThreadedBuilder.java:51)
at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:128)
at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:307)
at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:193)
at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:106)
at org.apache.maven.cli.MavenCli.execute(MavenCli.java:863)
at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:288)
at org.apache.maven.cli.MavenCli.main(MavenCli.java:199)
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)
at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:289)
at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:229)
at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:415)
at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:356)
Caused by: java.lang.IllegalArgumentException: Error in module 'bug-augment': can not resolve QNameModule for 'bt0:target'. Statement source at META-INF/yang/bug-augment.yang:14:2
at com.google.common.base.Preconditions.checkArgument(Preconditions.java:145)
at org.opendaylight.yangtools.yang.parser.stmt.rfc6020.Utils.qNameFromArgument(Utils.java:516)
at org.opendaylight.yangtools.yang.parser.stmt.rfc6020.Utils.nodeIdentifierFromPath(Utils.java:448)
... 45 more