set to null if empty tag specified

platform/util/src/com/intellij/util/xmlb/Binding.java

@@ -38,6 +38,10 @@ abstract class Binding {
   @Nullable
   public abstract Object deserialize(Object context, @NotNull Object node);
 
+  public Object deserializeEmpty(Object context) {
+    return null;
+  }
+
   public abstract boolean isBoundTo(Object node);
 
   public abstract Class getBoundNodeType();
@@ -52,8 +56,15 @@ abstract class Binding {
       return ((MultiNodeBinding)binding).deserializeList(context, nodes);
     }
     else {
-      assert nodes.size() == 1;
-      return binding.deserialize(context, nodes.get(0));
+      if (nodes.size() == 1) {
+        return binding.deserialize(context, nodes.get(0));
+      }
+      else if (nodes.isEmpty()) {
+        return binding.deserializeEmpty(context);
+      }
+      else {
+        throw new AssertionError("Duplicate data for " + binding + " will be ignored");
+      }
     }
   }
 }

platform/util/src/com/intellij/util/xmlb/DateBinding.java

@@ -37,16 +37,10 @@ public class DateBinding extends PrimitiveValueBinding {
   @Override
   protected Object convertString(String value) {
     try {
-      long l = Long.parseLong(value);
-      return new Date(l);
+      return new Date(Long.parseLong(value));
     }
     catch (NumberFormatException e) {
       return new Date(0);
     }
   }
-
-  @Override
-  public boolean isMulti() {
-    return false;
-  }
 }

platform/util/src/com/intellij/util/xmlb/JDOMElementBinding.java

@@ -71,15 +71,7 @@ class JDOMElementBinding extends Binding implements MultiNodeBinding {
       myAccessor.write(context, nodes.toArray(new Element[nodes.size()]));
     }
     else {
-      Element element = null;
-      for (Object aNode : nodes) {
-        if (!XmlSerializerImpl.isIgnoredNode(aNode)) {
-          element = (Element)aNode;
-          break;
-        }
-      }
-      assert element != null;
-      myAccessor.write(context, element);
+      myAccessor.write(context, nodes.get(0));
     }
     return context;
   }

platform/util/src/com/intellij/util/xmlb/PrimitiveValueBinding.java

@@ -21,9 +21,7 @@ import org.jdom.Text;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
-import java.util.List;
-
-class PrimitiveValueBinding extends Binding implements MultiNodeBinding {
+class PrimitiveValueBinding extends Binding {
   private final Class<?> myType;
 
   public PrimitiveValueBinding(@NotNull Class<?> myType, @Nullable Accessor accessor) {
@@ -37,35 +35,17 @@ class PrimitiveValueBinding extends Binding implements MultiNodeBinding {
     return new Text(String.valueOf(o));
   }
 
-  @Nullable
-  @Override
-  public Object deserializeList(Object context, @NotNull List<?> nodes) {
-    if (nodes.isEmpty()) {
-      return convertString("");
-    }
-    else if (nodes.size() > 1) {
-      StringBuilder result = new StringBuilder();
-      for (Object node : nodes) {
-        result.append(node instanceof Attribute ? ((Attribute)node).getValue() : ((Content)node).getValue());
-      }
-      return convertString(result.toString());
-    }
-    else {
-      return deserialize(context, nodes.get(0));
-    }
-  }
-
-  @Override
-  public boolean isMulti() {
-    return true;
-  }
-
   @Override
   @Nullable
   public Object deserialize(Object o, @NotNull Object node) {
     return convertString(node instanceof Attribute ? ((Attribute)node).getValue() : ((Content)node).getValue());
   }
 
+  @Override
+  public Object deserializeEmpty(Object context) {
+    return convertString("");
+  }
+
   @Nullable
   protected Object convertString(String value) {
     return XmlSerializerImpl.convert(value, myType);