FOP-3321: Improve error message when invalid PS setpagedevice used

src/main/java/org/apache/xmlgraphics/ps/PSDictionary.java

diff --git a/src/main/java/org/apache/xmlgraphics/ps/PSDictionary.java b/src/main/java/org/apache/xmlgraphics/ps/PSDictionary.java
index 965d694..5a95196 100644
--- a/src/main/java/org/apache/xmlgraphics/ps/PSDictionary.java
+++ b/src/main/java/org/apache/xmlgraphics/ps/PSDictionary.java
@@ -195,6 +195,9 @@
                     throw new PSDictionaryFormatException("Failed to parse object key");
                 }
                 Token valueToken = nextToken(str, keyToken.endIndex + 1);
+                if (valueToken == null) {
+                    throw new PSDictionaryFormatException("Failed to parse object value");
+                }
                 String[] braces = null;
                 for (String[] brace : BRACES) {
                     if (valueToken.value.startsWith(brace[OPENING])) {

src/test/java/org/apache/xmlgraphics/ps/PSDictionaryTestCase.java

diff --git a/src/test/java/org/apache/xmlgraphics/ps/PSDictionaryTestCase.java b/src/test/java/org/apache/xmlgraphics/ps/PSDictionaryTestCase.java
new file mode 100644
index 0000000..5ee0a6b
--- /dev/null
+++ b/src/test/java/org/apache/xmlgraphics/ps/PSDictionaryTestCase.java
@@ -0,0 +1,33 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.xmlgraphics.ps;
+
+import org.junit.Assert;
+import org.junit.Test;
+import org.junit.function.ThrowingRunnable;
+
+public class PSDictionaryTestCase {
+    @Test
+    public void testInvalidMediaPosition() {
+        Exception ex = Assert.assertThrows(PSDictionaryFormatException.class, new ThrowingRunnable() {
+                public void run() throws Throwable {
+                    PSDictionary.valueOf("<![CDATA[ << /MediaPosition   >> ]] >");
+                }
+            });
+        Assert.assertEquals("Failed to parse object value", ex.getMessage());
+    }
+}