public void removeField(final String key) {
        if (!RESERVED_FIELDS.contains(key)) {
            final Object removedValue = fields.remove(key);
            updateSize(key, null, removedValue);
        }
    }
@Test
    public void testRemoveField() throws Exception {
        message.addField("foo", "bar");

        message.removeField("foo");
        assertNull(message.getField("foo"));
    }