Unable to resolve grouping

module a {
  yang-version 1.1;
  namespace "a";
  prefix a;
  import b { prefix b;}

  grouping foo {
    container bar {
      leaf foo {
        type string;
      }
      uses software-operation-state;
    }

    grouping software-operation-state {
      leaf bar2 {
        type empty;
      }
      uses next-operation-group;
    }

    grouping next-operation-group {
      list next-operation {
         key order;
         config false;

         leaf order {
             description "A logical sequence number of operations to be done.";
             type uint8;
         }
         leaf operation-type {
             description "Type of software action launched on the device.";
             type string;
         }
         leaf software-name {
             description "Name of the software on which the operation was performed. For download operations, the leaf only records the software name and not the complete URL.";
             type string;
         }
      } // list next-operation
    }
  }
  augment "/b:fooo" {
    uses a:foo;
  }
}

module b {
  yang-version 1.1;
  namespace "b";
  prefix b;

  container fooo {
    leaf baar {
      type empty;
    }
  }
}

[ERROR] yang-to-sources: Unable to generate sources with org.opendaylight.mdsal.binding.maven.api.gen.plugin.CodeGeneratorImpl generator
java.lang.IllegalStateException: Grouping AbsoluteSchemaPath{path=[(a)foo, (a)next-operation-group]}is not resolved for SoftwareOperationState
    at org.opendaylight.mdsal.binding.generator.impl.AbstractTypeGenerator.addImplementedInterfaceFromUses (AbstractTypeGenerator.java:1887)
    at org.opendaylight.mdsal.binding.generator.impl.AbstractTypeGenerator.addDefaultInterfaceDefinition (AbstractTypeGenerator.java:1625)
    at org.opendaylight.mdsal.binding.generator.impl.AbstractTypeGenerator.addDefaultInterfaceDefinition (AbstractTypeGenerator.java:1593)
    at org.opendaylight.mdsal.binding.generator.impl.AbstractTypeGenerator.addDefaultInterfaceDefinition (AbstractTypeGenerator.java:1587)
    at org.opendaylight.mdsal.binding.generator.impl.AbstractTypeGenerator.groupingsToGenTypes (AbstractTypeGenerator.java:700)
    at org.opendaylight.mdsal.binding.generator.impl.AbstractTypeGenerator.addDefaultInterfaceDefinition (AbstractTypeGenerator.java:1624)
    at org.opendaylight.mdsal.binding.generator.impl.AbstractTypeGenerator.addDefaultInterfaceDefinition (AbstractTypeGenerator.java:1593)
    at org.opendaylight.mdsal.binding.generator.impl.AbstractTypeGenerator.processDataSchemaNode (AbstractTypeGenerator.java:281)
    at org.opendaylight.mdsal.binding.generator.impl.AbstractTypeGenerator.containerToGenType (AbstractTypeGenerator.java:299)
    at org.opendaylight.mdsal.binding.generator.impl.AbstractTypeGenerator.addSchemaNodeToBuilderAsMethod (AbstractTypeGenerator.java:1055)
    at org.opendaylight.mdsal.binding.generator.impl.AbstractTypeGenerator.resolveDataSchemaNodes (AbstractTypeGenerator.java:1004)
    at org.opendaylight.mdsal.binding.generator.impl.AbstractTypeGenerator.moduleToGenTypes (AbstractTypeGenerator.java:239)
    at org.opendaylight.mdsal.binding.generator.impl.AbstractTypeGenerator.<init> (AbstractTypeGenerator.java:200)
    at org.opendaylight.mdsal.binding.generator.impl.CodegenTypeGenerator.<init> (CodegenTypeGenerator.java:32)
    at org.opendaylight.mdsal.binding.generator.impl.BindingGeneratorImpl.generateTypes (BindingGeneratorImpl.java:64)
    at org.opendaylight.mdsal.binding.maven.api.gen.plugin.CodeGeneratorImpl.generateSources (CodeGeneratorImpl.java:70)
    at org.opendaylight.yangtools.yang2sources.plugin.YangToSourcesProcessor.generateSourcesWithOneGenerator (YangToSourcesProcessor.java:383)
    at org.opendaylight.yangtools.yang2sources.plugin.YangToSourcesProcessor.generateSources (YangToSourcesProcessor.java:332)
    at org.opendaylight.yangtools.yang2sources.plugin.YangToSourcesProcessor.conditionalExecute (YangToSourcesProcessor.java:159)
    at org.opendaylight.yangtools.yang2sources.plugin.YangToSourcesMojo.execute (YangToSourcesMojo.java:127)