Fix URI template operators 'prefix', 'suffix' and 'list' to return th…

…e empty string for undefined variables.

As per draft 3 of the URI template spec, made the the 'prefix', 'suffix' and 'list' to return the empty string for undefined variables.
Previously, 'prefix' and 'suffix' returned the arg regardless and 'list' raised an exception.

Added tests.  Ideally the next draft of the spec would include examples equivalent to these.

lib/addressable/uri.rb

@@ -461,7 +461,7 @@ def self.expand_prefix_operator(argument, variables, mapping)
       value = mapping[variables.first]
       if value.kind_of?(Array)
         (value.map { |list_value| argument + list_value }).join("")
-      else
+      elsif value
         argument + value.to_s
       end
     end
@@ -483,7 +483,7 @@ def self.expand_suffix_operator(argument, variables, mapping)
       value = mapping[variables.first]
       if value.kind_of?(Array)
         (value.map { |list_value| list_value + argument }).join("")
-      else
+      elsif value
         value.to_s + argument
       end
     end
@@ -526,7 +526,8 @@ def self.expand_list_operator(argument, variables, mapping)
         raise InvalidTemplateOperatorError,
           "Template operator 'list' takes exactly one variable."
       end
-      mapping[variables.first].join(argument)
+      values = mapping[variables.first]
+      values.join(argument) if values
     end
     class <<self; private :expand_list_operator; end
 

spec/addressable/uri_spec.rb

@@ -3697,6 +3697,36 @@ def self.transform(name, value)
   end
 end
 
+describe Addressable::URI, "when given an empty mapping" do
+  before do
+    @mapping = {}
+  end
+
+  it "should result in 'http://example.com/search/'" +
+      " when used to expand 'http://example.com/search/{-list|+|query}'" do
+    Addressable::URI.expand_template(
+      "http://example.com/search/{-list|+|query}",
+      @mapping).to_str.should ==
+        "http://example.com/search/"
+  end
+
+  it "should result in 'http://example.com'" +
+      " when used to expand 'http://example.com{-prefix|/|foo}'" do
+    Addressable::URI.expand_template(
+      "http://example.com{-prefix|/|foo}",
+      @mapping).to_str.should ==
+        "http://example.com"
+  end
+
+  it "should result in 'http://example.com'" +
+      " when used to expand 'http://example.com{-suffix|/|foo}'" do
+    Addressable::URI.expand_template(
+      "http://example.com{-suffix|/|foo}",
+      @mapping).to_str.should ==
+        "http://example.com"
+  end
+end
+
 class SuperString
   def initialize(string)
     @string = string.to_s