ExpansionPanel({@required ExpansionPanelHeaderBuilder headerBuilder, @required Widget body, bool isExpanded: false })

Creates an expansion panel to be used as a child for ExpansionPanelList.

None of the arguments can be null.

Source 

ExpansionPanel({
  @required this.headerBuilder,
  @required this.body,
  this.isExpanded: false
}) {
  assert(this.headerBuilder != null);
  assert(this.body != null);
  assert(this.isExpanded != null);
}