BUG-9265: Switch empty type mapping from Void to Empty

Using Void means NormalizedNode.getValue() has to be nullable,
which wreaks havoc to a lot of places. Switch mapping to Empty, which
is a singleton dedicated to representing this type.

This flushes out quite a few of null violations, which are also fixed
up.

Change-Id: I4de3afed3d641eda292fdd4116497f3f22a0d770
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>

yang/yang-data-api/src/main/java/org/opendaylight/yangtools/yang/data/api/codec/EmptyCodec.java

@@ -8,11 +8,12 @@
 package org.opendaylight.yangtools.yang.data.api.codec;
 
 import org.opendaylight.yangtools.concepts.Codec;
+import org.opendaylight.yangtools.yang.common.Empty;
 
-public interface EmptyCodec<T>  extends Codec<T,Void> {
+public interface EmptyCodec<T> extends Codec<T, Empty> {
     @Override
-    T serialize(Void data);
+    T serialize(Empty data);
 
     @Override
-    Void deserialize(T data);
+    Empty deserialize(T data);
 }

yang/yang-data-api/src/main/java/org/opendaylight/yangtools/yang/data/api/codec/StringCodec.java

@@ -7,12 +7,13 @@
  */
 package org.opendaylight.yangtools.yang.data.api.codec;
 
+import javax.annotation.Nonnull;
 import org.opendaylight.yangtools.concepts.Codec;
 
 public interface StringCodec<T> extends Codec<T,String> {
     @Override
-    T serialize(String data);
+    T serialize(@Nonnull String data);
 
     @Override
-    String deserialize(T data);
+    String deserialize(@Nonnull T data);
 }

yang/yang-data-api/src/main/java/org/opendaylight/yangtools/yang/data/api/schema/AnyXmlNode.java

@@ -7,6 +7,7 @@
  */
 package org.opendaylight.yangtools.yang.data.api.schema;
 
+import javax.annotation.Nonnull;
 import javax.xml.transform.dom.DOMSource;
 import org.opendaylight.yangtools.yang.data.api.AttributesContainer;
 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier.NodeIdentifier;
@@ -15,16 +16,12 @@
  * AN normalizedNode.
  */
 public interface AnyXmlNode extends AttributesContainer, DataContainerChild<NodeIdentifier, DOMSource> {
-
-    @Override
-    NodeIdentifier getIdentifier();
-
     /**
      * Return value represented as a DOMSource. Returned source contains top level element
      * that duplicates the anyxml node.
      *
      * @return anyxml node value represented as DOMSource.
      */
     @Override
-    DOMSource getValue();
+    @Nonnull DOMSource getValue();
 }

yang/yang-data-api/src/main/java/org/opendaylight/yangtools/yang/data/api/schema/AugmentationNode.java

@@ -8,6 +8,7 @@
 package org.opendaylight.yangtools.yang.data.api.schema;
 
 import java.util.Collection;
+import javax.annotation.Nonnull;
 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier.AugmentationIdentifier;
 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier.PathArgument;
 import org.opendaylight.yangtools.yang.model.api.AugmentationSchema;
@@ -34,8 +35,8 @@ public interface AugmentationNode extends MixinNode, DataContainerNode<Augmentat
      * This is sufficient to identify instance of augmentation, since RFC6020 states that <code>augment</code>
      * that augment statement must not add multiple nodes from same namespace / module to the target node.
      *
-     * @return Identifier which uniquelly identifies augmentation in particular subtree.
+     * @return Identifier which uniquely identifies augmentation in particular subtree.
      */
     @Override
-    AugmentationIdentifier getIdentifier();
+    @Nonnull AugmentationIdentifier getIdentifier();
 }

yang/yang-data-api/src/main/java/org/opendaylight/yangtools/yang/data/api/schema/DataContainerChild.java

@@ -7,6 +7,7 @@
  */
 package org.opendaylight.yangtools.yang.data.api.schema;
 
+import javax.annotation.Nonnull;
 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier.PathArgument;
 
 /**
@@ -29,5 +30,5 @@
  */
 public interface DataContainerChild<K extends PathArgument,V> extends NormalizedNode<K, V> {
     @Override
-    K getIdentifier();
+    @Nonnull K getIdentifier();
 }

yang/yang-data-api/src/main/java/org/opendaylight/yangtools/yang/data/api/schema/DataContainerNode.java

@@ -8,6 +8,7 @@
 package org.opendaylight.yangtools.yang.data.api.schema;
 
 import java.util.Collection;
+import javax.annotation.Nonnull;
 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier.PathArgument;
 
 /**
@@ -41,5 +42,5 @@ public interface DataContainerNode<K extends PathArgument> extends //
      * @return Iteration of all child nodes
      */
     @Override
-    Collection<DataContainerChild<? extends PathArgument, ?>> getValue();
+    @Nonnull Collection<DataContainerChild<? extends PathArgument, ?>> getValue();
 }

yang/yang-data-api/src/main/java/org/opendaylight/yangtools/yang/data/api/schema/LeafNode.java

@@ -7,6 +7,7 @@
  */
 package org.opendaylight.yangtools.yang.data.api.schema;
 
+import javax.annotation.Nonnull;
 import org.opendaylight.yangtools.yang.data.api.AttributesContainer;
 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier.NodeIdentifier;
 
@@ -27,5 +28,5 @@ public interface LeafNode<T> extends AttributesContainer, DataContainerChild<Nod
      * @return Returned value of this leaf node. Value SHOULD meet criteria defined by schema.
      */
     @Override
-    T getValue();
+    @Nonnull T getValue();
 }

yang/yang-data-api/src/main/java/org/opendaylight/yangtools/yang/data/api/schema/LeafSetEntryNode.java

@@ -7,6 +7,7 @@
  */
 package org.opendaylight.yangtools.yang.data.api.schema;
 
+import javax.annotation.Nonnull;
 import org.opendaylight.yangtools.yang.data.api.AttributesContainer;
 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier.NodeWithValue;
 
@@ -38,5 +39,5 @@ public interface LeafSetEntryNode<T> extends AttributesContainer, NormalizedNode
      * @return {@link NodeWithValue} which identifies this leaf set entry.
      */
     @Override
-    NodeWithValue getIdentifier();
+    @Nonnull NodeWithValue getIdentifier();
 }

yang/yang-data-api/src/main/java/org/opendaylight/yangtools/yang/data/api/schema/LeafSetNode.java

@@ -20,9 +20,7 @@
  *
  * @param <T> Type of leaf node values.
  */
-public interface LeafSetNode<T> extends
-    MixinNode, //
-    DataContainerChild<NodeIdentifier, Collection<LeafSetEntryNode<T>>>, //
-    NormalizedNodeContainer<NodeIdentifier, NodeWithValue,LeafSetEntryNode<T>> {
+public interface LeafSetNode<T> extends MixinNode, DataContainerChild<NodeIdentifier, Collection<LeafSetEntryNode<T>>>,
+    NormalizedNodeContainer<NodeIdentifier, NodeWithValue, LeafSetEntryNode<T>> {
 
 }

yang/yang-data-api/src/main/java/org/opendaylight/yangtools/yang/data/api/schema/NormalizedNode.java

@@ -7,6 +7,7 @@
  */
 package org.opendaylight.yangtools.yang.data.api.schema;
 
+import javax.annotation.Nonnull;
 import org.opendaylight.yangtools.concepts.Identifiable;
 import org.opendaylight.yangtools.yang.common.QName;
 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier.PathArgument;
@@ -35,12 +36,12 @@ public interface NormalizedNode<K extends PathArgument, V> extends Identifiable<
      * @return Node identifier, non-null.
      */
     @Override
-    K getIdentifier();
+    @Nonnull K getIdentifier();
 
     /**
      * Value of node.
      *
      * @return Value of the node, may be null.
      */
-    V getValue();
+    @Nonnull V getValue();
 }

yang/yang-data-api/src/main/java/org/opendaylight/yangtools/yang/data/api/schema/ValueNode.java

@@ -7,6 +7,7 @@
  */
 package org.opendaylight.yangtools.yang.data.api.schema;
 
+import javax.annotation.Nonnull;
 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier.PathArgument;
 
 /**
@@ -30,5 +31,5 @@ public interface ValueNode<K extends PathArgument, V> extends NormalizedNode<K,
      *
      */
     @Override
-    V getValue();
+    @Nonnull V getValue();
 }

yang/yang-data-codec-gson/src/main/java/org/opendaylight/yangtools/yang/data/codec/gson/EmptyJSONCodec.java

@@ -10,8 +10,9 @@
 
 import com.google.gson.stream.JsonWriter;
 import java.io.IOException;
+import org.opendaylight.yangtools.yang.common.Empty;
 
-final class EmptyJSONCodec implements JSONCodec<Void> {
+final class EmptyJSONCodec implements JSONCodec<Empty> {
 
     static final EmptyJSONCodec INSTANCE = new EmptyJSONCodec();
 
@@ -20,17 +21,17 @@ private EmptyJSONCodec() {
     }
 
     @Override
-    public Class<Void> getDataType() {
-        return Void.class;
+    public Class<Empty> getDataType() {
+        return Empty.class;
     }
 
     @Override
-    public Void parseValue(final Object ctx, final String input) {
-        return null;
+    public Empty parseValue(final Object ctx, final String input) {
+        return Empty.getInstance();
     }
 
     @Override
-    public void writeValue(final JsonWriter ctx, final Void value) throws IOException {
+    public void writeValue(final JsonWriter ctx, final Empty value) throws IOException {
         ctx.beginArray();
         ctx.value((String) null);
         ctx.endArray();

yang/yang-data-codec-gson/src/test/java/org/opendaylight/yangtools/yang/data/codec/gson/JsonStreamToNormalizedNodeTest.java

@@ -24,6 +24,7 @@
 import java.util.Collections;
 import org.junit.BeforeClass;
 import org.junit.Test;
+import org.opendaylight.yangtools.yang.common.Empty;
 import org.opendaylight.yangtools.yang.common.QName;
 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier.AugmentationIdentifier;
 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier.NodeIdentifier;
@@ -164,7 +165,7 @@ public void emptyTypeTest() throws IOException, URISyntaxException {
         final String inputJson = loadTextFile("/complexjson/type-empty.json");
         final ContainerNode awaitedStructure = containerBuilder()
                 .withNodeIdentifier(new NodeIdentifier(CONT_1))
-                .addChild(leafNode(EMPTY_LEAF, null))
+                .addChild(leafNode(EMPTY_LEAF, Empty.getInstance()))
                 .build();
 
         verifyTransformationToNormalizedNode(inputJson, awaitedStructure);

yang/yang-data-codec-gson/src/test/java/org/opendaylight/yangtools/yang/data/codec/gson/NormalizedNodeToJsonStreamTest.java

@@ -29,6 +29,7 @@
 import java.util.Iterator;
 import org.junit.BeforeClass;
 import org.junit.Test;
+import org.opendaylight.yangtools.yang.common.Empty;
 import org.opendaylight.yangtools.yang.common.QName;
 import org.opendaylight.yangtools.yang.data.api.YangInstanceIdentifier;
 import org.opendaylight.yangtools.yang.data.api.schema.ContainerNode;
@@ -297,7 +298,7 @@ public void emptyTypeTest() throws IOException, URISyntaxException {
         final StringWriter writer = new StringWriter();
         final ContainerNode emptyStructure = Builders.containerBuilder()
                 .withNodeIdentifier(new YangInstanceIdentifier.NodeIdentifier(CONT_1))
-                .addChild(ImmutableNodes.leafNode(EMPTY_LEAF, null)).build();
+                .addChild(ImmutableNodes.leafNode(EMPTY_LEAF, Empty.getInstance())).build();
         final String jsonOutput = normalizedNodeToJsonStreamTransformation(writer, emptyStructure);
         final JsonObject cont1 = resolveCont1(jsonOutput);
         final JsonElement emptyObj = cont1.get("empty");

yang/yang-data-codec-xml/src/main/java/org/opendaylight/yangtools/yang/data/codec/xml/EmptyXmlCodec.java

@@ -5,14 +5,16 @@
  * terms of the Eclipse Public License v1.0 which accompanies this distribution,
  * and is available at http://www.eclipse.org/legal/epl-v10.html
  */
-
 package org.opendaylight.yangtools.yang.data.codec.xml;
 
+import static java.util.Objects.requireNonNull;
+
 import javax.xml.namespace.NamespaceContext;
 import javax.xml.stream.XMLStreamException;
 import javax.xml.stream.XMLStreamWriter;
+import org.opendaylight.yangtools.yang.common.Empty;
 
-final class EmptyXmlCodec implements XmlCodec<Void> {
+final class EmptyXmlCodec implements XmlCodec<Empty> {
 
     static final EmptyXmlCodec INSTANCE = new EmptyXmlCodec();
 
@@ -21,17 +23,18 @@ private EmptyXmlCodec() {
     }
 
     @Override
-    public Class<Void> getDataType() {
-        return Void.class;
+    public Class<Empty> getDataType() {
+        return Empty.class;
     }
 
     @Override
-    public Void parseValue(final NamespaceContext ctx, final String str) {
-        return null;
+    public Empty parseValue(final NamespaceContext ctx, final String str) {
+        return Empty.getInstance();
     }
 
     @Override
-    public void writeValue(final XMLStreamWriter ctx, final Void value) throws XMLStreamException {
+    public void writeValue(final XMLStreamWriter ctx, final Empty value) throws XMLStreamException {
+        requireNonNull(value);
         ctx.writeCharacters("");
     }
 }

yang/yang-data-impl/src/main/java/org/opendaylight/yangtools/yang/data/impl/codec/EmptyStringCodec.java

@@ -8,28 +8,30 @@
 package org.opendaylight.yangtools.yang.data.impl.codec;
 
 import static com.google.common.base.Preconditions.checkArgument;
+import static java.util.Objects.requireNonNull;
 
-import com.google.common.base.Strings;
 import java.util.Optional;
+import org.opendaylight.yangtools.yang.common.Empty;
 import org.opendaylight.yangtools.yang.data.api.codec.EmptyCodec;
 import org.opendaylight.yangtools.yang.model.api.type.EmptyTypeDefinition;
 
-final class EmptyStringCodec extends TypeDefinitionAwareCodec<Void, EmptyTypeDefinition> implements
+final class EmptyStringCodec extends TypeDefinitionAwareCodec<Empty, EmptyTypeDefinition> implements
         EmptyCodec<String> {
     static final EmptyStringCodec INSTANCE = new EmptyStringCodec();
 
     private EmptyStringCodec() {
-        super(Optional.empty(), Void.class);
+        super(Optional.empty(), Empty.class);
     }
 
     @Override
-    public String serialize(final Void data) {
+    public String serialize(final Empty data) {
+        requireNonNull(data);
         return "";
     }
 
     @Override
-    public Void deserialize(final String stringRepresentation) {
-        checkArgument(Strings.isNullOrEmpty(stringRepresentation), "The value must be empty");
-        return null;
+    public Empty deserialize(final String stringRepresentation) {
+        checkArgument(stringRepresentation.isEmpty(), "The value must be empty");
+        return Empty.getInstance();
     }
 }

yang/yang-data-impl/src/main/java/org/opendaylight/yangtools/yang/data/impl/codec/StringStringCodec.java

@@ -8,14 +8,14 @@
 package org.opendaylight.yangtools.yang.data.impl.codec;
 
 import static com.google.common.base.Preconditions.checkArgument;
+import static java.util.Objects.requireNonNull;
 
 import com.google.common.annotations.Beta;
 import com.google.common.collect.ImmutableRangeSet;
 import com.google.common.collect.Range;
 import com.google.common.collect.RangeSet;
 import com.google.common.collect.TreeRangeSet;
 import java.util.Collection;
-import java.util.Objects;
 import java.util.Optional;
 import org.opendaylight.yangtools.yang.data.api.codec.StringCodec;
 import org.opendaylight.yangtools.yang.model.api.type.LengthConstraint;
@@ -56,17 +56,13 @@ public static StringStringCodec from(final StringTypeDefinition normalizedType)
 
     @Override
     public final String deserialize(final String stringRepresentation) {
-        if (stringRepresentation == null) {
-            // FIXME: These seems buggy, but someone may be using this behaviour
-            return "";
-        }
-        validate(stringRepresentation);
+        validate(requireNonNull(stringRepresentation));
         return stringRepresentation;
     }
 
     @Override
     public final String serialize(final String data) {
-        return Objects.toString(data, "");
+        return requireNonNull(data);
     }
 
     void validate(final String str) {