Fixed the value of empty YAML nodes being written as "null". Thanks rcjrrjcr!

By: EvilSeph <evilseph@unaligned.org>

paper-api/src/main/java/org/bukkit/util/config/Configuration.java

@@ -10,7 +10,15 @@ import java.util.Map;
 import org.yaml.snakeyaml.DumperOptions;
 import org.yaml.snakeyaml.Yaml;
 import org.yaml.snakeyaml.constructor.SafeConstructor;
+import org.yaml.snakeyaml.introspector.Property;
+import org.yaml.snakeyaml.nodes.CollectionNode;
+import org.yaml.snakeyaml.nodes.MappingNode;
+import org.yaml.snakeyaml.nodes.Node;
+import org.yaml.snakeyaml.nodes.NodeTuple;
+import org.yaml.snakeyaml.nodes.SequenceNode;
+import org.yaml.snakeyaml.nodes.Tag;
 import org.yaml.snakeyaml.reader.UnicodeReader;
+import org.yaml.snakeyaml.representer.Represent;
 import org.yaml.snakeyaml.representer.Representer;
 
 /**
@@ -44,7 +52,6 @@ import org.yaml.snakeyaml.representer.Representer;
  * <p>This class is currently incomplete. It is not yet possible to get a node.
  * </p>
  *
- * @author sk89q
  */
 public class Configuration extends ConfigurationNode {
     private Yaml yaml;
@@ -58,7 +65,7 @@ public class Configuration extends ConfigurationNode {
         options.setIndent(4);
         options.setDefaultFlowStyle(DumperOptions.FlowStyle.BLOCK);
 
-        yaml = new Yaml(new SafeConstructor(), new Representer(), options);
+        yaml = new Yaml(new SafeConstructor(), new EmptyNullRepresenter(), options);
 
         this.file = file;
     }
@@ -136,3 +143,41 @@ public class Configuration extends ConfigurationNode {
         return new ConfigurationNode(new HashMap<String, Object>());
     }
 }
+
+class EmptyNullRepresenter extends Representer {
+
+    public EmptyNullRepresenter() {
+        super();
+        this.nullRepresenter = new EmptyRepresentNull();
+    }
+
+    protected class EmptyRepresentNull implements Represent {
+        public Node representData(Object data) {
+            return representScalar(Tag.NULL, ""); // Changed "null" to "" so as to avoid writing nulls
+        }
+    }
+
+    // Code borrowed from snakeyaml (http://code.google.com/p/snakeyaml/source/browse/src/test/java/org/yaml/snakeyaml/issues/issue60/SkipBeanTest.java)
+    @Override
+    protected NodeTuple representJavaBeanProperty(Object javaBean, Property property, Object propertyValue, Tag customTag) {
+        NodeTuple tuple = super.representJavaBeanProperty(javaBean, property, propertyValue, customTag);
+        Node valueNode = tuple.getValueNode();
+        if (valueNode instanceof CollectionNode) {
+            // Removed null check
+            if (Tag.SEQ.equals(valueNode.getTag())) {
+                SequenceNode seq = (SequenceNode) valueNode;
+                if (seq.getValue().isEmpty()) {
+                    return null; // skip empty lists
+                }
+            }
+            if (Tag.MAP.equals(valueNode.getTag())) {
+                MappingNode seq = (MappingNode) valueNode;
+                if (seq.getValue().isEmpty()) {
+                    return null; // skip empty maps
+                }
+            }
+        }
+        return tuple;
+    }
+    // End of borrowed code
+}