diff --git a/src/main/java/com/reandroid/apk/xmlencoder/EncodeMaterials.java b/src/main/java/com/reandroid/apk/xmlencoder/EncodeMaterials.java
index 6677b10..eed5511 100644
--- a/src/main/java/com/reandroid/apk/xmlencoder/EncodeMaterials.java
+++ b/src/main/java/com/reandroid/apk/xmlencoder/EncodeMaterials.java
@@ -84,6 +84,10 @@
              if(ref!=null){
                  return ref.value;
              }
+             ref = ValueDecoder.encodeNullReference(refString);
+             if(ref!=null){
+                 return ref.value;
+             }
              throw new EncodeException(
                      "Not proper reference string: '"+refString+"'");
          }
diff --git a/src/main/java/com/reandroid/apk/xmlencoder/XMLValuesEncoderStyle.java b/src/main/java/com/reandroid/apk/xmlencoder/XMLValuesEncoderStyle.java
index ea75dfa..17ecd8d 100644
--- a/src/main/java/com/reandroid/apk/xmlencoder/XMLValuesEncoderStyle.java
+++ b/src/main/java/com/reandroid/apk/xmlencoder/XMLValuesEncoderStyle.java
@@ -39,11 +39,14 @@ class XMLValuesEncoderStyle extends XMLValuesEncoderBag{
             if(id!=0){
                 item.setName(id);
                 String value = child.getTextContent();
-                if(ValueDecoder.isReference(value)){
+                ValueDecoder.EncodeResult encodeResult = ValueDecoder.encodeNullReference(value);
+                if(encodeResult!=null){
+                    item.setTypeAndData(encodeResult.valueType, encodeResult.value);
+                }else if(ValueDecoder.isReference(value)){
                     item.setTypeAndData(ValueType.REFERENCE,
                             getMaterials().resolveReference(value));
                 }else {
-                    ValueDecoder.EncodeResult encodeResult = ValueDecoder.encodeGuessAny(value);
+                    encodeResult = ValueDecoder.encodeGuessAny(value);
                     if(encodeResult!=null){
                         item.setTypeAndData(encodeResult.valueType, encodeResult.value);
                     }else {
@@ -86,6 +89,11 @@ class XMLValuesEncoderStyle extends XMLValuesEncoderBag{
             bagItem.setTypeAndData(encodeEnumFlag.valueType, encodeEnumFlag.value);
             return;
         }
+        ValueDecoder.EncodeResult encodeResult = ValueDecoder.encodeNullReference(valueText);
+        if(encodeResult!=null){
+            bagItem.setTypeAndData(encodeResult.valueType, encodeResult.value);
+            return;
+        }
         if(ValueDecoder.isReference(valueText)){
             if(valueText.startsWith("?")){
                 bagItem.setValueType(ValueType.ATTRIBUTE);
@@ -99,7 +107,7 @@ class XMLValuesEncoderStyle extends XMLValuesEncoderBag{
         }else if(EncodeUtil.isEmpty(valueText)) {
             bagItem.setTypeAndData(ValueType.NULL, 0);
         }else{
-            ValueDecoder.EncodeResult encodeResult = ValueDecoder.encodeGuessAny(valueText);
+            encodeResult = ValueDecoder.encodeGuessAny(valueText);
             if(encodeResult!=null){
                 bagItem.setTypeAndData(encodeResult.valueType,
                         encodeResult.value);
diff --git a/src/main/java/com/reandroid/arsc/decoder/ValueDecoder.java b/src/main/java/com/reandroid/arsc/decoder/ValueDecoder.java
index d60f89a..c100bb8 100755
--- a/src/main/java/com/reandroid/arsc/decoder/ValueDecoder.java
+++ b/src/main/java/com/reandroid/arsc/decoder/ValueDecoder.java
@@ -63,16 +63,11 @@ public class ValueDecoder {
         if(txt==null){
             return null;
         }
-        if("@empty".equals(txt)){
-            return new EncodeResult(ValueType.NULL, 1);
+        EncodeResult result = encodeNullReference(txt);
+        if(result != null){
+            return result;
         }
-        if("@null".equals(txt)){
-            return new EncodeResult(ValueType.REFERENCE, 0);
-        }
-        if("?null".equals(txt)){
-            return new EncodeResult(ValueType.ATTRIBUTE, 0);
-        }
-        EncodeResult result=encodeColor(txt);
+        result=encodeColor(txt);
         if(result!=null){
             return result;
         }
@@ -99,6 +94,21 @@ public class ValueDecoder {
         }
         return null;
     }
+    public static EncodeResult encodeNullReference(String txt){
+        if(txt==null){
+            return null;
+        }
+        if("@empty".equals(txt)){
+            return new EncodeResult(ValueType.NULL, 1);
+        }
+        if("@null".equals(txt)){
+            return new EncodeResult(ValueType.REFERENCE, 0);
+        }
+        if("?null".equals(txt)){
+            return new EncodeResult(ValueType.ATTRIBUTE, 0);
+        }
+        return null;
+    }
     public static EncodeResult encodeHexReference(String txt){
         if(txt==null){
             return null;