lib/sycamore/exceptions.rb in sycamore-0.1.0 vs lib/sycamore/exceptions.rb in sycamore-0.2.0

@@ -1,10 +1,16 @@
 module Sycamore
   # raised when a value is not a valid node
   class InvalidNode < ArgumentError ; end
+
   # raised when trying to call a additive command method of the {Nothing} tree
   class NothingMutation < StandardError ; end
-  # raised when calling {Tree#node} on a Tree with multiple nodes
+
+  # raised when calling {Tree#node} or {Tree#node!} on a Tree with multiple nodes
   class NonUniqueNodeSet < StandardError ; end
+
+  # raised when calling {Tree#node!} on a Tree without nodes
+  class EmptyNodeSet < StandardError ; end
+
   # raised when trying to fetch the child of a leaf
   class ChildError < KeyError ; end
 end