message: Prevent exception on unset when dropState is null
diff: @@ -133,6 +133,7 @@ function install (scope: Scope) {
  const { dropState } = interaction
  + if (dropState) {
  dropState.activeDrops = null
  dropState.events = null
  dropState.cur.dropzone = null
  @@ -140,6 +141,7 @@ function install (scope: Scope) {
  dropState.prev.dropzone = null
  dropState.prev.element = null
  dropState.rejected = false
  + }
  })
  /**
  