--- a/jaxp/src/java.xml/share/classes/javax/xml/catalog/CatalogResolverImpl.java	Thu Jun 02 23:26:41 2016 -0700
+++ b/jaxp/src/java.xml/share/classes/javax/xml/catalog/CatalogResolverImpl.java	Fri Jun 03 11:38:38 2016 -0700
@@ -51,6 +51,7 @@
 
     @Override
     public InputSource resolveEntity(String publicId, String systemId) {
+        CatalogMessages.reportNPEOnNull("systemId", systemId);
         //Normalize publicId and systemId
         systemId = Normalizer.normalizeURI(Util.getNotNullOrEmpty(systemId));
         publicId = Normalizer.normalizePublicId(Normalizer.decodeURN(Util.getNotNullOrEmpty(publicId)));

--- a/jaxp/test/javax/xml/jaxp/libs/catalog/ResolutionChecker.java	Thu Jun 02 23:26:41 2016 -0700
+++ b/jaxp/test/javax/xml/jaxp/libs/catalog/ResolutionChecker.java	Fri Jun 03 11:38:38 2016 -0700
@@ -41,7 +41,7 @@
     static void checkExtIdResolution(CatalogResolver resolver,
             String publicId, String systemId, String matchedUri) {
         Assert.assertEquals(
-                resolver.resolveEntity(publicId, systemId).getSystemId(),
+                resolver.resolveEntity(publicId, getNotSpecified(systemId)).getSystemId(),
                 matchedUri);
     }
 
@@ -95,7 +95,7 @@
      * CatalogUriResolver should throw CatalogException.
      */
     static void checkNoMatch(CatalogUriResolver resolver) {
-        resolver.resolve("http://uri/noMatch/docNoMatch.dtd", null);
+        resolver.resolve("http://uri/noMatch/docNoMatch.dtd", getNotSpecified(null));
     }
 
     /* ********** Checks expected exception ********** */
@@ -108,7 +108,7 @@
             CatalogResolver resolver, String publicId, String systemId,
             Class<T> expectedExceptionClass) {
         expectThrows(expectedExceptionClass, () -> {
-            resolver.resolveEntity(publicId, systemId);
+            resolver.resolveEntity(publicId, getNotSpecified(systemId));
         });
     }
 
@@ -181,6 +181,18 @@
         throw new AssertionError(message);
     }
 
+    /*
+     * SystemId can never be null in XML. For publicId tests, if systemId is null,
+     * it will be considered as not-specified instead. A non-existent systemId
+     * is returned to make sure there's no match by the systemId.
+    */
+    private static String getNotSpecified(String systemId) {
+        if (systemId == null) {
+            return "not-specified-systemId.dtd";
+        }
+        return systemId;
+    }
+
     private interface ThrowingRunnable {
         void run() throws Throwable;
     }

--- a/jaxp/test/javax/xml/jaxp/unittest/catalog/CatalogTest.java	Thu Jun 02 23:26:41 2016 -0700
+++ b/jaxp/test/javax/xml/jaxp/unittest/catalog/CatalogTest.java	Fri Jun 03 11:38:38 2016 -0700
@@ -69,6 +69,20 @@
     }
 
     /*
+     * @bug 8150187
+     * NPE is expected if the systemId is null. The specification for systemId
+     * is as follows:
+     * A system identifier is required on all external entities. XML
+     * requires a system identifier on all external entities, so this value is
+     * always specified.
+     */
+    @Test(expectedExceptions = NullPointerException.class)
+    public void sysIdCantBeNull() {
+        CatalogResolver catalogResolver = CatalogManager.catalogResolver(CatalogFeatures.defaults());
+        InputSource is = catalogResolver.resolveEntity("-//FOO//DTD XML Dummy V0.0//EN", null);
+    }
+
+    /*
      * @bug 8156845
      * Verifies that an URI reference with a urn:publicid is correctly resolved
      * with an uri entry with a publicId.