diff --git a/app/src/main/java/org/fdroid/fdroid/data/AppProvider.java b/app/src/main/java/org/fdroid/fdroid/data/AppProvider.java
index 4116638bb..96475ea42 100644
--- a/app/src/main/java/org/fdroid/fdroid/data/AppProvider.java
+++ b/app/src/main/java/org/fdroid/fdroid/data/AppProvider.java
@@ -572,7 +572,7 @@ public class AppProvider extends FDroidProvider {
     public static Uri getSearchUri(Repo repo, String query) {
         return getContentUri().buildUpon()
             .appendPath(PATH_SEARCH_REPO)
-            .appendPath(repo.id + "")
+            .appendPath(String.valueOf(repo.id))
             .appendPath(query)
             .build();
     }
diff --git a/app/src/main/java/org/fdroid/fdroid/net/LocalHTTPD.java b/app/src/main/java/org/fdroid/fdroid/net/LocalHTTPD.java
index 23937b9ec..d6d2f7633 100644
--- a/app/src/main/java/org/fdroid/fdroid/net/LocalHTTPD.java
+++ b/app/src/main/java/org/fdroid/fdroid/net/LocalHTTPD.java
@@ -221,7 +221,7 @@ public class LocalHTTPD extends NanoHTTPD {
         try {
             // Calculate etag
             String etag = Integer
-                    .toHexString((file.getAbsolutePath() + file.lastModified() + "" + file.length())
+                    .toHexString((file.getAbsolutePath() + file.lastModified() + String.valueOf(file.length()))
                             .hashCode());
 
             // Support (simple) skipping:
@@ -268,7 +268,7 @@ public class LocalHTTPD extends NanoHTTPD {
                     fis.skip(startFrom);
 
                     res = createResponse(Response.Status.PARTIAL_CONTENT, mime, fis);
-                    res.addHeader("Content-Length", "" + dataLen);
+                    res.addHeader("Content-Length", String.valueOf(dataLen));
                     res.addHeader("Content-Range", "bytes " + startFrom + "-" + endAt + "/"
                             + fileLen);
                     res.addHeader("ETag", etag);
@@ -278,7 +278,7 @@ public class LocalHTTPD extends NanoHTTPD {
                     res = createResponse(Response.Status.NOT_MODIFIED, mime, "");
                 } else {
                     res = createResponse(Response.Status.OK, mime, new FileInputStream(file));
-                    res.addHeader("Content-Length", "" + fileLen);
+                    res.addHeader("Content-Length", String.valueOf(fileLen));
                     res.addHeader("ETag", etag);
                 }
             }
diff --git a/app/src/main/java/org/fdroid/fdroid/net/bluetooth/BluetoothServer.java b/app/src/main/java/org/fdroid/fdroid/net/bluetooth/BluetoothServer.java
index 811508992..dc935199f 100644
--- a/app/src/main/java/org/fdroid/fdroid/net/bluetooth/BluetoothServer.java
+++ b/app/src/main/java/org/fdroid/fdroid/net/bluetooth/BluetoothServer.java
@@ -259,7 +259,7 @@ public class BluetoothServer extends Thread {
             try {
                 // Calculate etag
                 String etag = Integer
-                        .toHexString((file.getAbsolutePath() + file.lastModified() + "" + file.length())
+                        .toHexString((file.getAbsolutePath() + file.lastModified() + String.valueOf(file.length()))
                                 .hashCode());
 
                 // Support (simple) skipping:
@@ -306,7 +306,7 @@ public class BluetoothServer extends Thread {
                         fis.skip(startFrom);
 
                         res = createResponse(NanoHTTPD.Response.Status.PARTIAL_CONTENT, mime, fis);
-                        res.addHeader("Content-Length", "" + dataLen);
+                        res.addHeader("Content-Length", String.valueOf(dataLen));
                         res.addHeader("Content-Range", "bytes " + startFrom + "-" + endAt + "/"
                                 + fileLen);
                         res.addHeader("ETag", etag);
@@ -316,7 +316,7 @@ public class BluetoothServer extends Thread {
                         res = createResponse(NanoHTTPD.Response.Status.NOT_MODIFIED, mime, "");
                     } else {
                         res = createResponse(NanoHTTPD.Response.Status.OK, mime, new FileInputStream(file));
-                        res.addHeader("Content-Length", "" + fileLen);
+                        res.addHeader("Content-Length", String.valueOf(fileLen));
                         res.addHeader("ETag", etag);
                     }
                 }
diff --git a/config/pmd/rules.xml b/config/pmd/rules.xml
index 314281ed0..fbde9c171 100644
--- a/config/pmd/rules.xml
+++ b/config/pmd/rules.xml
@@ -16,4 +16,5 @@
         <exclude name="UselessParentheses"/> <!--Too nitpicky-->
     </rule>
     <rule ref="rulesets/java/optimizations.xml/PrematureDeclaration"/>
+    <rule ref="rulesets/java/optimizations.xml/AddEmptyString"/>
 </ruleset>