[ERROR] yang-to-sources: Unable to generate sources with org.opendaylight.mdsal.binding.maven.api.gen.plugin.CodeGeneratorImpl generator
java.lang.IllegalArgumentException: Failed to find prefix for statement (urn:example:module2?revision=2019-05-17)ext1
    at com.google.common.base.Preconditions.checkArgument (Preconditions.java:210)
    at org.opendaylight.yangtools.yang.model.export.ExportUtils.statementPrefix (ExportUtils.java:62)
    at org.opendaylight.yangtools.yang.model.export.YangTextSnippetIterator.pushStatement (YangTextSnippetIterator.java:199)
    at org.opendaylight.yangtools.yang.model.export.YangTextSnippetIterator.computeNext (YangTextSnippetIterator.java:160)
    at org.opendaylight.yangtools.yang.model.export.YangTextSnippetIterator.computeNext (YangTextSnippetIterator.java:42)
    at com.google.common.collect.AbstractIterator.tryToComputeNext (AbstractIterator.java:140)
    at com.google.common.collect.AbstractIterator.hasNext (AbstractIterator.java:135)
    at org.opendaylight.mdsal.binding.java.api.generator.BaseTemplate.appendYangSnippet (BaseTemplate.java:424)
    at org.opendaylight.mdsal.binding.java.api.generator.BaseTemplate.appendSnippet (BaseTemplate.java:391)
    at org.opendaylight.mdsal.binding.java.api.generator.BaseTemplate.formatDataForJavaDoc (BaseTemplate.java:342)
    at org.opendaylight.mdsal.binding.java.api.generator.InterfaceTemplate.body (InterfaceTemplate.java:73)
    at org.opendaylight.mdsal.binding.java.api.generator.BaseTemplate.generate (BaseTemplate.java:88)
    at org.opendaylight.mdsal.binding.java.api.generator.InterfaceGenerator.generate (InterfaceGenerator.java:34)
    at org.opendaylight.mdsal.binding.java.api.generator.GeneratorJavaFile$GeneratorStringSupplier.get (GeneratorJavaFile.java:54)
    at org.opendaylight.mdsal.binding.java.api.generator.GeneratorJavaFile$GeneratorStringSupplier.get (GeneratorJavaFile.java:43)
    at org.opendaylight.mdsal.binding.maven.api.gen.plugin.CodeGeneratorImpl.generateSources (CodeGeneratorImpl.java:113)
    at org.opendaylight.yangtools.yang2sources.plugin.YangToSourcesProcessor.generateSourcesWithOneGenerator (YangToSourcesProcessor.java:380)
    at org.opendaylight.yangtools.yang2sources.plugin.YangToSourcesProcessor.generateSources (YangToSourcesProcessor.java:330)
    at org.opendaylight.yangtools.yang2sources.plugin.YangToSourcesProcessor.conditionalExecute (YangToSourcesProcessor.java:157)
    at org.opendaylight.yangtools.yang2sources.plugin.YangToSourcesMojo.execute (YangToSourcesMojo.java:124)
    at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo (DefaultBuildPluginManager.java:137)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:210)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:156)
    at org.apache.maven.lifecycle.internal.MojoExecutor.execute (MojoExecutor.java:148)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:117)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:81)
    at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build (SingleThreadedBuilder.java:56)
    at org.apache.maven.lifecycle.internal.LifecycleStarter.execute (LifecycleStarter.java:128)
    at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:305)
    at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:192)
    at org.apache.maven.DefaultMaven.execute (DefaultMaven.java:105)
    at org.apache.maven.cli.MavenCli.execute (MavenCli.java:956)
    at org.apache.maven.cli.MavenCli.doMain (MavenCli.java:288)
    at org.apache.maven.cli.MavenCli.main (MavenCli.java:192)
    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)
[ERROR] yang-to-sources: One or more code generators failed, including failed list(generatorClass=exception) {org.opendaylight.mdsal.binding.maven.api.gen.plugin.CodeGeneratorImpl=java.lang.IllegalArgumentException}