emptySelectionAllowed property
final
Determines if having no selected segments is allowed.
If true, then it is acceptable for none of the segments to be selected. This means that selected can be empty. If the user taps on a selected segment, it will be removed from the selection set passed into onSelectionChanged.
If false (the default), there must be at least one segment selected. If the user taps on the only selected segment it will not be deselected, and onSelectionChanged will not be called.
Implementation
final bool emptySelectionAllowed;