Fix invalid language options wrapper.

Author: chumer

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/runtime/PythonOptions.java

@@ -368,7 +368,11 @@ public int hashCode() {
 
         @SuppressWarnings("unchecked")
         public <T> T get(OptionKey<T> optionKey) {
-            return (T) engineOptions.get(optionKey);
+            if (engineOptions.containsKey(optionKey)) {
+                return (T) engineOptions.get(optionKey);
+            } else {
+                return optionKey.getDefaultValue();
+            }
         }
 
         public boolean hasBeenSet(OptionKey<?> optionKey) {