Handle nil labels

src/spectator/block.cr

@@ -16,7 +16,7 @@ module Spectator
     # The *proc* will be called to evaluate the value of the expression.
     # The *label* is usually the Crystal code for the *proc*.
     # It can be nil if it isn't available.
-    def initialize(@block : -> T, label : Label)
+    def initialize(@block : -> T, label : Label = nil)
       super(label)
     end
 
@@ -24,7 +24,7 @@ module Spectator
     # The block will be called to evaluate the value of the expression.
     # The *label* is usually the Crystal code for the *block*.
     # It can be nil if it isn't available.
-    def initialize(label : Label, &@block : -> T)
+    def initialize(label : Label = nil, &@block : -> T)
       super(label)
     end
 

src/spectator/value.cr

@@ -14,9 +14,16 @@ module Spectator
     # Creates the value.
     # Expects the *value* of the expression and a *label* describing it.
     # The *label* is usually the Crystal code evaluating to the *value*.
-    # It can be nil if it isn't available.
     def initialize(@value : T, label : Label)
       super(label)
     end
+
+    # Creates the value.
+    # Expects the *value* of the expression.
+    # It can be nil if it isn't available.
+    # A label is generated by calling `#inspect` on the *value*.
+    def initialize(@value : T)
+      super(@value.inspect)
+    end
   end
 end