add Maybe::optionalValue

Add a method to retrieve the value stored in a Maybe as a Java Optional.

Author: michi42

src/java/org/tensorics/core/util/Maybe.java

@@ -116,6 +116,21 @@ public T value() {
         return value;
     }
 
+    /**
+     * Retrieve the value stored in this {@link Maybe} as an {@link Optional}. If an exception is stored in this Maybe,
+     * the returned optional will be empty. For a "successful" {@link Maybe}<Void>, it will contain null.
+     * 
+     * @return the value
+     * @throws RuntimeException if this Maybe objects contains an exception
+     */
+    public Optional<T> optionalValue() {
+        if (exception != null) {
+            return Optional.empty();
+        } else {
+            return Optional.of(value);
+        }
+    }
+
     /**
      * Throw the contained exception, wrapped in a {@link RuntimeException}, if any. If called on a "successful" Maybe,
      * this method does nothing.
@@ -308,4 +323,4 @@ public String toString() {
         }
     }
 
-}
+}