diff --git a/lib/server-core/src/main/java/org/apache/olingo/server/core/debug/DebugResponseHelperImpl.java b/lib/server-core/src/main/java/org/apache/olingo/server/core/debug/DebugResponseHelperImpl.java
index 7c0d617f2..aec88586f 100644
--- a/lib/server-core/src/main/java/org/apache/olingo/server/core/debug/DebugResponseHelperImpl.java
+++ b/lib/server-core/src/main/java/org/apache/olingo/server/core/debug/DebugResponseHelperImpl.java
@@ -21,6 +21,7 @@ package org.apache.olingo.server.core.debug;
 import java.io.ByteArrayInputStream;
 import java.io.IOException;
 import java.io.InputStream;
+import java.io.OutputStream;
 import java.io.StringWriter;
 import java.io.Writer;
 import java.util.ArrayList;
@@ -133,11 +134,13 @@ public class DebugResponseHelperImpl implements DebugResponseHelper {
   }
 
   private InputStream wrapInJson(final List<DebugTab> parts) throws IOException {
-    CircleStreamBuffer csb = new CircleStreamBuffer();
     IOException cachedException = null;
+    OutputStream outputStream = null;
 
     try {
-      JsonGenerator gen = new JsonFactory().createGenerator(csb.getOutputStream(), JsonEncoding.UTF8);
+      CircleStreamBuffer csb = new CircleStreamBuffer();
+      outputStream = csb.getOutputStream();
+      JsonGenerator gen = new JsonFactory().createGenerator(outputStream, JsonEncoding.UTF8);
 
       gen.writeStartObject();
       DebugTab requestInfo = parts.get(0);
@@ -159,14 +162,15 @@ public class DebugResponseHelperImpl implements DebugResponseHelper {
 
       gen.writeEndObject();
       gen.close();
-      csb.getOutputStream().close();
+      outputStream.close();
 
+      return csb.getInputStream();
     } catch (IOException e) {
       throw e;
     } finally {
-      if (csb != null && csb.getOutputStream() != null) {
+      if (outputStream != null) {
         try {
-          csb.getOutputStream().close();
+          outputStream.close();
         } catch (IOException e) {
           if (cachedException != null) {
             throw cachedException;
@@ -176,8 +180,6 @@ public class DebugResponseHelperImpl implements DebugResponseHelper {
         }
       }
     }
-
-    return csb.getInputStream();
   }
 
   /**
diff --git a/lib/server-core/src/main/java/org/apache/olingo/server/core/debug/DebugTabUri.java b/lib/server-core/src/main/java/org/apache/olingo/server/core/debug/DebugTabUri.java
index 9953ceeb2..5e1a92158 100644
--- a/lib/server-core/src/main/java/org/apache/olingo/server/core/debug/DebugTabUri.java
+++ b/lib/server-core/src/main/java/org/apache/olingo/server/core/debug/DebugTabUri.java
@@ -19,6 +19,8 @@
 package org.apache.olingo.server.core.debug;
 
 import java.io.IOException;
+import java.io.InputStream;
+import java.io.OutputStream;
 import java.io.Writer;
 import java.util.List;
 
@@ -256,19 +258,20 @@ public class DebugTabUri implements DebugTab {
   private String getJsonString() throws IOException {
     CircleStreamBuffer csb = new CircleStreamBuffer();
     IOException cachedException = null;
+    OutputStream outputStream = csb.getOutputStream();
     try {
       JsonGenerator json =
-          new JsonFactory().createGenerator(csb.getOutputStream(), JsonEncoding.UTF8)
+          new JsonFactory().createGenerator(outputStream, JsonEncoding.UTF8)
               .setPrettyPrinter(new DefaultPrettyPrinter());
       appendJson(json);
       json.close();
-      csb.getOutputStream().close();
+      outputStream.close();
     } catch (IOException e) {
       throw e;
     } finally {
-      if (csb != null && csb.getOutputStream() != null) {
+      if (outputStream != null) {
         try {
-          csb.getOutputStream().close();
+          outputStream.close();
         } catch (IOException e) {
           if (cachedException != null) {
             throw cachedException;
@@ -279,16 +282,17 @@ public class DebugTabUri implements DebugTab {
       }
     }
 
+    InputStream inputStream = csb.getInputStream();
     try {
-      String jsonString = IOUtils.toString(csb.getInputStream());
-      csb.getInputStream().close();
+      String jsonString = IOUtils.toString(inputStream);
+      inputStream.close();
       return jsonString;
     } catch (IOException e) {
       throw e;
     } finally {
-      if (csb != null && csb.getInputStream() != null) {
+      if (inputStream != null) {
         try {
-          csb.getInputStream().close();
+          inputStream.close();
         } catch (IOException e) {
           if (cachedException != null) {
             throw cachedException;
diff --git a/lib/server-core/src/main/java/org/apache/olingo/server/core/serializer/json/ODataJsonSerializer.java b/lib/server-core/src/main/java/org/apache/olingo/server/core/serializer/json/ODataJsonSerializer.java
index 8c18f8f03..57fc4712b 100644
--- a/lib/server-core/src/main/java/org/apache/olingo/server/core/serializer/json/ODataJsonSerializer.java
+++ b/lib/server-core/src/main/java/org/apache/olingo/server/core/serializer/json/ODataJsonSerializer.java
@@ -21,6 +21,7 @@ package org.apache.olingo.server.core.serializer.json;
 import java.io.IOException;
 import java.io.OutputStream;
 import java.util.Collections;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
 
@@ -83,7 +84,7 @@ public class ODataJsonSerializer extends AbstractODataSerializer {
   public SerializerResult serviceDocument(final ServiceMetadata metadata, final String serviceRoot)
       throws SerializerException {
     OutputStream outputStream = null;
-    SerializerException cachedException = null;
+    SerializerException cachedException = null; 
 
     try {
       CircleStreamBuffer buffer = new CircleStreamBuffer();
@@ -319,7 +320,7 @@ public class ODataJsonSerializer extends AbstractODataSerializer {
       final SelectOption select, final JsonGenerator json)
       throws IOException, SerializerException {
     final boolean all = ExpandSelectHelper.isAll(select);
-    final Set<String> selected = all ? null :
+    final Set<String> selected = all ? new HashSet<String>() :
         ExpandSelectHelper.getSelectedPropertyNames(select.getSelectItems());
     for (final String propertyName : type.getPropertyNames()) {
       if (all || selected.contains(propertyName)) {
@@ -337,7 +338,7 @@ public class ODataJsonSerializer extends AbstractODataSerializer {
       final JsonGenerator json) throws SerializerException, IOException {
     if (ExpandSelectHelper.hasExpand(expand)) {
       final boolean expandAll = ExpandSelectHelper.isExpandAll(expand);
-      final Set<String> expanded = expandAll ? null :
+      final Set<String> expanded = expandAll ? new HashSet<String>() :
           ExpandSelectHelper.getExpandedPropertyNames(expand.getExpandItems());
       for (final String propertyName : type.getNavigationPropertyNames()) {
         if (expandAll || expanded.contains(propertyName)) {
diff --git a/lib/server-core/src/main/java/org/apache/olingo/server/core/serializer/xml/ODataXmlSerializer.java b/lib/server-core/src/main/java/org/apache/olingo/server/core/serializer/xml/ODataXmlSerializer.java
index 547c45f36..b40d4efa4 100644
--- a/lib/server-core/src/main/java/org/apache/olingo/server/core/serializer/xml/ODataXmlSerializer.java
+++ b/lib/server-core/src/main/java/org/apache/olingo/server/core/serializer/xml/ODataXmlSerializer.java
@@ -22,6 +22,7 @@ import java.io.IOException;
 import java.io.OutputStream;
 import java.text.SimpleDateFormat;
 import java.util.Date;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Set;
 
@@ -495,7 +496,7 @@ public class ODataXmlSerializer extends AbstractODataSerializer {
       final List<Property> properties, final SelectOption select, final XMLStreamWriter writer)
       throws XMLStreamException, SerializerException {
     final boolean all = ExpandSelectHelper.isAll(select);
-    final Set<String> selected = all ? null :
+    final Set<String> selected = all ? new HashSet<String>() :
         ExpandSelectHelper.getSelectedPropertyNames(select.getSelectItems());
     for (final String propertyName : type.getPropertyNames()) {
       if (all || selected.contains(propertyName)) {
@@ -513,7 +514,7 @@ public class ODataXmlSerializer extends AbstractODataSerializer {
       final XMLStreamWriter writer) throws SerializerException, XMLStreamException {
     if (ExpandSelectHelper.hasExpand(expand)) {
       final boolean expandAll = ExpandSelectHelper.isExpandAll(expand);
-      final Set<String> expanded = expandAll ? null :
+      final Set<String> expanded = expandAll ? new HashSet<String>() :
           ExpandSelectHelper.getExpandedPropertyNames(expand.getExpandItems());
       for (final String propertyName : type.getNavigationPropertyNames()) {
         final EdmNavigationProperty property = type.getNavigationProperty(propertyName);