do not save null in text and extra text

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

@@ -32,6 +32,7 @@ public class TextBinding implements Binding {
   @Override
   public Object serialize(Object o, Object context, SerializationFilter filter) {
     final Object v = myAccessor.read(o);
+    if (v == null) return context;
     final Object node = myBinding.serialize(v, context, filter);
 
     return new Text(((Content)node).getValue());

platform/util/testSrc/com/intellij/util/xmlb/XmlSerializerTest.java

@@ -1029,6 +1029,31 @@ public class XmlSerializerTest extends TestCase {
     }
   }
 
+  public static class ConversionFromTextToAttributeBean {
+    @Property(surroundWithTag = false)
+    public ConditionBean myConditionBean = new ConditionBean();
+  }
+  @Tag("condition")
+  public static class ConditionBean {
+    @Attribute("expression")
+    public String myNewCondition;
+    @Text
+    public String myOldCondition;
+  }
+
+  public void testConversionFromTextToAttribute() {
+    ConversionFromTextToAttributeBean bean = new ConversionFromTextToAttributeBean();
+    bean.myConditionBean.myOldCondition = "2+2";
+    doSerializerTest("<ConversionFromTextToAttributeBean>\n" +
+                     "  <condition>2+2</condition>\n" +
+                     "</ConversionFromTextToAttributeBean>", bean);
+
+    bean = new ConversionFromTextToAttributeBean();
+    bean.myConditionBean.myNewCondition = "2+2";
+    doSerializerTest("<ConversionFromTextToAttributeBean>\n" +
+                     "  <condition expression=\"2+2\" />\n" +
+                     "</ConversionFromTextToAttributeBean>", bean);
+  }
 
   public void testDeserializeInto() throws Exception {
     BeanWithPublicFields bean = new BeanWithPublicFields();