Fix object marking of arrays in zlib.

Author: aardvark179

src/main/java/org/truffleruby/cext/CExtNodes.java

@@ -76,6 +76,7 @@
 import org.truffleruby.interop.TranslateInteropExceptionNode;
 import org.truffleruby.core.string.ImmutableRubyString;
 import org.truffleruby.language.LexicalScope;
+import org.truffleruby.language.Nil;
 import org.truffleruby.language.RubyBaseNode;
 import org.truffleruby.language.RubyDynamicObject;
 import org.truffleruby.language.RubyGuards;
@@ -2055,6 +2056,11 @@ public abstract static class DataHolderGetMarker extends PrimitiveArrayArguments
         protected Object getMarker(DataHolder data) {
             return data.getMarker();
         }
+
+        @Specialization
+        protected Object getMarker(Nil data) {
+            return data;
+        }
     }
 
     @Primitive(name = "data_holder_set_marker")