When a leaf has a union type, and a default that does not correspond to the first member of that union type, the default is not processed correctly. The attached model gives an error:

Caused by: org.opendaylight.yangtools.yang.parser.spi.source.SourceException: Unable to find a default value for leaf '(http://www.example.com?revision=2017-07-10)enum-last-leaf' [at example-model:35:4]
at org.opendaylight.yangtools.yang.parser.stmt.rfc6020.effective.LeafEffectiveStatementImpl.(LeafEffectiveStatementImpl.java:67)
at org.opendaylight.yangtools.yang.parser.stmt.rfc6020.LeafStatementImpl$Definition.createEffective(LeafStatementImpl.java:79)
at org.opendaylight.yangtools.yang.parser.stmt.reactor.StatementContextBase.buildEffective(StatementContextBase.java:408)
at com.google.common.collect.Iterators$8.transform(Iterators.java:799)
at com.google.common.collect.TransformedIterator.next(TransformedIterator.java:48)
at java.util.AbstractCollection.toArray(AbstractCollection.java:141)
at com.google.common.collect.ImmutableList.copyOf(ImmutableList.java:258)
at org.opendaylight.yangtools.yang.parser.stmt.rfc6020.effective.EffectiveStatementBase.(EffectiveStatementBase.java:56)
at org.opendaylight.yangtools.yang.parser.stmt.rfc6020.effective.DeclaredEffectiveStatementBase.(DeclaredEffectiveStatementBase.java:32)
at org.opendaylight.yangtools.yang.parser.stmt.rfc6020.effective.AbstractEffectiveDocumentedNode.(AbstractEffectiveDocumentedNode.java:30)
at org.opendaylight.yangtools.yang.parser.stmt.rfc6020.effective.AbstractEffectiveDocumentedDataNodeContainer.(AbstractEffectiveDocumentedDataNodeContainer.java:45)
at org.opendaylight.yangtools.yang.parser.stmt.rfc6020.effective.AbstractEffectiveSimpleDataNodeContainer.(AbstractEffectiveSimpleDataNodeContainer.java:47)
at org.opendaylight.yangtools.yang.parser.stmt.rfc6020.effective.AbstractEffectiveContainerSchemaNode.(AbstractEffectiveContainerSchemaNode.java:21)
at org.opendaylight.yangtools.yang.parser.stmt.rfc6020.effective.ContainerEffectiveStatementImpl.(ContainerEffectiveStatementImpl.java:32)
at org.opendaylight.yangtools.yang.parser.stmt.rfc6020.ContainerStatementImpl$Definition.createEffective(ContainerStatementImpl.java:86)
at org.opendaylight.yangtools.yang.parser.stmt.reactor.StatementContextBase.buildEffective(StatementContextBase.java:408)
at com.google.common.collect.Iterators$8.transform(Iterators.java:799)
at com.google.common.collect.TransformedIterator.next(TransformedIterator.java:48)
at java.util.AbstractCollection.toArray(AbstractCollection.java:141)
at com.google.common.collect.ImmutableList.copyOf(ImmutableList.java:258)
at org.opendaylight.yangtools.yang.parser.stmt.rfc6020.effective.EffectiveStatementBase.(EffectiveStatementBase.java:56)
at org.opendaylight.yangtools.yang.parser.stmt.rfc6020.effective.DeclaredEffectiveStatementBase.(DeclaredEffectiveStatementBase.java:32)
at org.opendaylight.yangtools.yang.parser.stmt.rfc6020.effective.AbstractEffectiveDocumentedNode.(AbstractEffectiveDocumentedNode.java:30)
at org.opendaylight.yangtools.yang.parser.stmt.rfc6020.effective.AbstractEffectiveModule.(AbstractEffectiveModule.java:86)
at org.opendaylight.yangtools.yang.parser.stmt.rfc6020.effective.ModuleEffectiveStatementImpl.(ModuleEffectiveStatementImpl.java:23)
at org.opendaylight.yangtools.yang.parser.stmt.rfc6020.ModuleStatementSupport.createEffective(ModuleStatementSupport.java:100)
at org.opendaylight.yangtools.yang.parser.stmt.reactor.StatementContextBase.buildEffective(StatementContextBase.java:408)
at org.opendaylight.yangtools.yang.parser.stmt.reactor.BuildGlobalContext.transformEffective(BuildGlobalContext.java:250)
... 80 more
Caused by: java.lang.IllegalStateException: Unable to find following default values [any]
at com.google.common.base.Preconditions.checkState(Preconditions.java:197)
at org.opendaylight.yangtools.yang.parser.stmt.rfc6020.TypeUtils.isAnyDefaultValueMarkedWithIfFeature(TypeUtils.java:305)
at org.opendaylight.yangtools.yang.parser.stmt.rfc6020.TypeUtils.isAnyDefaultValueMarkedWithIfFeature(TypeUtils.java:300)
at org.opendaylight.yangtools.yang.parser.stmt.rfc6020.TypeUtils.isAnyDefaultValueMarkedWithIfFeature(TypeUtils.java:300)
at org.opendaylight.yangtools.yang.parser.stmt.rfc6020.TypeUtils.hasDefaultValueMarkedWithIfFeature(TypeUtils.java:277)
at org.opendaylight.yangtools.yang.parser.stmt.rfc6020.effective.LeafEffectiveStatementImpl.(LeafEffectiveStatementImpl.java:61)
... 107 more

This is because TypeUtils.isAnyDefaultValueMarkedWithIfFeature is called recursively, but bails out after the first member type of the union.