Add check for custom Number in U.subtract(values).

Author: javadev

src/main/java/com/github/underscore/lodash/U.java

@@ -1136,6 +1136,8 @@ public static <T extends Number> T subtract(final T ... values) {
                 result = add(result, (T) Long.valueOf(values[i].longValue() * -1));
             } else if (result instanceof Short) {
                 result = add(result, (T) Short.valueOf((short) (values[i].shortValue() * -1)));
+            } else {
+                throw new UnsupportedOperationException("Subtract only supports official subclasses of Number");
             }
         }
         return result;

src/test/java/com/github/underscore/lodash/MathTest.java

@@ -276,7 +276,7 @@ public void subtract() {
         assertEquals(null, U.subtract());
     }
 
-    @Test
+    @Test(expected = UnsupportedOperationException.class)
     public void subtractError() {
         class MyNumber extends Number {
             public int intValue() {