Re-submitting: Unset config properties: `System.getProperty` should return default value or null (previously reverted)#10096

niloc132 merged 2 commits intomaingwtproject/gwt:mainfrom

revert-10094-revert-10013-config-propgwtproject/gwt:revert-10094-revert-10013-config-propCopy head branch name to clipboard