PDFBOX-6076: avoid ClassCastexception, use ON as default

git-svn-id: https://svn.apache.org/repos/asf/pdfbox/trunk@1928739 13f79535-47bb-0310-9956-ffa450edef68

Author: THausherr

pdfbox/src/main/java/org/apache/pdfbox/pdmodel/graphics/optionalcontent/PDOptionalContentProperties.java

@@ -112,6 +112,11 @@ public COSDictionary getCOSObject()
         return this.dict;
     }
 
+    /**
+     * Return the /OCGs array.
+     * 
+     * @return /OCGs array, never null.
+     */
     private COSArray getOCGs()
     {
         COSArray ocgs = this.dict.getCOSArray(COSName.OCGS);
@@ -123,6 +128,11 @@ private COSArray getOCGs()
         return ocgs;
     }
 
+    /**
+     * Return the the /D dictionary.
+     *
+     * @return the /D dictionary, never null.
+     */
     private COSDictionary getD()
     {
         COSDictionary d = dict.getCOSDictionary(COSName.D);
@@ -202,12 +212,12 @@ public Collection<PDOptionalContentGroup> getOptionalContentGroups()
 
     /**
      * Returns the base state for optional content groups.
-     * @return the base state
+     * @return the base state, never null.
      */
     public BaseState getBaseState()
     {
         COSDictionary d = getD();
-        COSName name = (COSName)d.getItem(COSName.BASE_STATE);
+        COSName name = d.getCOSName(COSName.BASE_STATE, COSName.ON);
         return BaseState.valueOf(name);
     }