Binding Java API Generator -> NPE during code generation from specific yang models (package name is null for UnionType)

[ERROR] yang-to-sources: Unable to generate sources with org.opendaylight.yangtools.maven.sal.api.gen.plugin.CodeGeneratorImpl generator
java.lang.IllegalArgumentException: Type cannot have Package Name referenced as NULL!
at com.google.common.base.Preconditions.checkArgument(Preconditions.java:88)
at org.opendaylight.yangtools.sal.java.api.generator.GeneratorUtil.putTypeIntoImports(GeneratorUtil.java:138)

package name cannot be null, problem with hard-coded UnionType class:

public static final class UnionType implements Type {
@Override
public String getPackageName() {
return null;
.
.
.
.
.