diff --git a/hadoop-yarn-project/CHANGES.txt b/hadoop-yarn-project/CHANGES.txt
index b6e3b863766..21597b58ed9 100644
--- a/hadoop-yarn-project/CHANGES.txt
+++ b/hadoop-yarn-project/CHANGES.txt
@@ -271,6 +271,8 @@ Release 2.8.0 - UNRELEASED
     YARN-3343. Increased TestCapacitySchedulerNodeLabelUpdate#testNodeUpdate
     timeout. (Rohith Sharmaks via jianhe)
 
+    YARN-3582. NPE in WebAppProxyServlet. (jian he via xgong)
+
 Release 2.7.1 - UNRELEASED
 
   INCOMPATIBLE CHANGES
diff --git a/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-web-proxy/src/main/java/org/apache/hadoop/yarn/server/webproxy/WebAppProxyServlet.java b/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-web-proxy/src/main/java/org/apache/hadoop/yarn/server/webproxy/WebAppProxyServlet.java
index fd98c80592d..d45beb68d77 100644
--- a/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-web-proxy/src/main/java/org/apache/hadoop/yarn/server/webproxy/WebAppProxyServlet.java
+++ b/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-web-proxy/src/main/java/org/apache/hadoop/yarn/server/webproxy/WebAppProxyServlet.java
@@ -248,8 +248,11 @@ public class WebAppProxyServlet extends HttpServlet {
       final String remoteUser = req.getRemoteUser();
       final String pathInfo = req.getPathInfo();
 
-      String[] parts = pathInfo.split("/", 3);
-      if(parts.length < 2) {
+      String[] parts = null;
+      if (pathInfo != null) {
+        parts = pathInfo.split("/", 3);
+      }
+      if(parts == null || parts.length < 2) {
         LOG.warn("{} gave an invalid proxy path {}", remoteUser,  pathInfo);
         notFound(resp, "Your path appears to be formatted incorrectly.");
         return;
diff --git a/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-web-proxy/src/test/java/org/apache/hadoop/yarn/server/webproxy/TestWebAppProxyServlet.java b/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-web-proxy/src/test/java/org/apache/hadoop/yarn/server/webproxy/TestWebAppProxyServlet.java
index aa6d918bcb1..2a2ca2ca3d2 100644
--- a/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-web-proxy/src/test/java/org/apache/hadoop/yarn/server/webproxy/TestWebAppProxyServlet.java
+++ b/hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-web-proxy/src/test/java/org/apache/hadoop/yarn/server/webproxy/TestWebAppProxyServlet.java
@@ -131,6 +131,13 @@ public class TestWebAppProxyServlet {
 
     // wrong url
     try {
+      // wrong url without app ID
+      URL emptyUrl = new URL("http://localhost:" + proxyPort + "/proxy");
+      HttpURLConnection emptyProxyConn = (HttpURLConnection) emptyUrl
+          .openConnection();
+      emptyProxyConn.connect();;
+      assertEquals(HttpURLConnection.HTTP_NOT_FOUND, emptyProxyConn.getResponseCode());
+
       // wrong url. Set wrong app ID
       URL wrongUrl = new URL("http://localhost:" + proxyPort + "/proxy/app");
       HttpURLConnection proxyConn = (HttpURLConnection) wrongUrl