diff --git a/app/src/processing/app/Base.java b/app/src/processing/app/Base.java
index 62c2db364..1bd519769 100644
--- a/app/src/processing/app/Base.java
+++ b/app/src/processing/app/Base.java
@@ -2604,12 +2604,15 @@ public class Base {
                              File targetDir) throws IOException {
     targetDir.mkdirs();
     String files[] = sourceDir.list();
-    for (int i = 0; i < files.length; i++) {
+    if (files == null) {
+      throw new IOException("Unable to list files from " + sourceDir);
+    }
+    for (String file : files) {
       // Ignore dot files (.DS_Store), dot folders (.svn) while copying
-      if (files[i].charAt(0) == '.') continue;
+      if (file.charAt(0) == '.') continue;
       //if (files[i].equals(".") || files[i].equals("..")) continue;
-      File source = new File(sourceDir, files[i]);
-      File target = new File(targetDir, files[i]);
+      File source = new File(sourceDir, file);
+      File target = new File(targetDir, file);
       if (source.isDirectory()) {
         //target.mkdirs();
         copyDir(source, target);
diff --git a/app/src/processing/app/tools/Archiver.java b/app/src/processing/app/tools/Archiver.java
index c0f533023..81a60e41b 100644
--- a/app/src/processing/app/tools/Archiver.java
+++ b/app/src/processing/app/tools/Archiver.java
@@ -150,6 +150,9 @@ public class Archiver implements Tool {
   public void buildZip(File dir, String sofar,
                        ZipOutputStream zos) throws IOException {
     String files[] = dir.list();
+    if (files == null) {
+      throw new IOException("Unable to list files from " + dir);
+    }
     for (int i = 0; i < files.length; i++) {
       if (files[i].equals(".") ||
           files[i].equals("..")) continue;
diff --git a/arduino-core/src/processing/app/BaseNoGui.java b/arduino-core/src/processing/app/BaseNoGui.java
index 938c36768..9ae944cfe 100644
--- a/arduino-core/src/processing/app/BaseNoGui.java
+++ b/arduino-core/src/processing/app/BaseNoGui.java
@@ -956,14 +956,18 @@ public class BaseNoGui {
     if (!dir.exists()) return;
 
     String files[] = dir.list();
-    for (int i = 0; i < files.length; i++) {
-      if (files[i].equals(".") || files[i].equals("..")) continue;
-      File dead = new File(dir, files[i]);
+    if (files == null) {
+      return;
+    }
+
+    for (String file : files) {
+      if (file.equals(".") || file.equals("..")) continue;
+      File dead = new File(dir, file);
       if (!dead.isDirectory()) {
         if (!PreferencesData.getBoolean("compiler.save_build_files")) {
           if (!dead.delete()) {
             // temporarily disabled
-        System.err.println(I18n.format(_("Could not delete {0}"), dead));
+            System.err.println(I18n.format(_("Could not delete {0}"), dead));
           }
         }
       } else {
diff --git a/arduino-core/src/processing/app/SketchData.java b/arduino-core/src/processing/app/SketchData.java
index 36f5a8fce..677edcc80 100644
--- a/arduino-core/src/processing/app/SketchData.java
+++ b/arduino-core/src/processing/app/SketchData.java
@@ -95,6 +95,9 @@ public class SketchData {
 
     // get list of files in the sketch folder
     String list[] = folder.list();
+    if (list == null) {
+      throw new IOException("Unable to list files from " + folder);
+    }
 
     // reset these because load() may be called after an
     // external editor event. (fix for 0099)
diff --git a/arduino-core/src/processing/app/debug/Compiler.java b/arduino-core/src/processing/app/debug/Compiler.java
index e99414465..d6ecbcfd6 100644
--- a/arduino-core/src/processing/app/debug/Compiler.java
+++ b/arduino-core/src/processing/app/debug/Compiler.java
@@ -277,11 +277,13 @@ public class Compiler implements MessageConsumer {
       // used.  Keep everything else, which might be reusable
       if (tempBuildFolder.exists()) {
         String files[] = tempBuildFolder.list();
-        for (String file : files) {
-          if (file.endsWith(".c") || file.endsWith(".cpp") || file.endsWith(".s")) {
-            File deleteMe = new File(tempBuildFolder, file);
-            if (!deleteMe.delete()) {
-              System.err.println("Could not delete " + deleteMe);
+        if (files != null) {
+          for (String file : files) {
+            if (file.endsWith(".c") || file.endsWith(".cpp") || file.endsWith(".s")) {
+              File deleteMe = new File(tempBuildFolder, file);
+              if (!deleteMe.delete()) {
+                System.err.println("Could not delete " + deleteMe);
+              }
             }
           }
         }