Header hamburger button should be optional

[brunnerh]

Currently it always shows the button on small displays, even if there is no side nav. From the documentation:

Hamburger menu: The hamburger icon is used to open product navigation such as the left panel. The hamburger menu is only needed when there is a collapsable left navigation.

The example given on that page also has no side menu.

Since the navigation component is specified outside the header, it might be necessary to add a separate property or make isSideNavOpen have three meaningful states and use that to hide the button (it could accept null or undefined for example, maybe should be the default then).

[jquesada2016]

I 100% agree with this observation.