gistfile1.txt

index 57b442a..8264475 100644
--- a/lib/trollop.rb
+++ b/lib/trollop.rb
@@ -362,7 +362,7 @@ class Parser
       params = given_data[:params]
 
       opts = @specs[sym]
-      raise CommandlineError, "option '#{arg}' needs a parameter" if params.empty? && opts[:type] != :flag
+      raise CommandlineError, "option '#{arg}' needs a parameter" if params.empty? && opts[:type] != :flag and not opts[:allow_blank]
 
       vals["#{sym}_given".intern] = true # mark argument as specified on the commandline
 
@@ -383,7 +383,7 @@ class Parser
 
       if SINGLE_ARG_TYPES.include?(opts[:type])
         unless opts[:multi]       # single parameter
-          vals[sym] = vals[sym][0][0]
+          vals[sym] = vals[sym][0][0] rescue nil
         else                      # multiple options, each with a single parameter
           vals[sym] = vals[sym].map { |p| p[0] }
         end
diff --git a/test/test_trollop.rb b/test/test_trollop.rb
index 687c209..78d554b 100644
--- a/test/test_trollop.rb
+++ b/test/test_trollop.rb
@@ -42,14 +42,16 @@ class Trollop < ::Test::Unit::TestCase
     assert_raise(CommandlineError) { @p.parse(%w(--arg2 --arg3)) }
   end
   
-  ## flags that take an argument error unless given one
+  ## flags that take an argument error unless given one unless the argument is optional
   def test_argflags_demand_args
     @p.opt "goodarg", "desc", :type => String
     @p.opt "goodarg2", "desc", :type => String
-
+    @p.opt "goodarg3", "desc", :type => String, :allow_blank => true
+    
     assert_nothing_raised { @p.parse(%w(--goodarg goat)) }
     assert_raise(CommandlineError) { @p.parse(%w(--goodarg --goodarg2 goat)) }
     assert_raise(CommandlineError) { @p.parse(%w(--goodarg)) }
+    assert_nothing_raised { @p.parse(%w(--goodarg3)) }
   end
 
   ## flags that don't take arguments ignore them