diff --git a/ChangeLog b/ChangeLog
index c4ba0b9d..c951a193 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,15 @@
+2008-12-04  Tatsuhiro Tsujikawa  <t-tujikawa@users.sourceforge.net>
+
+	Added Option::blank().
+	Use !Option::blank(name) instead of Option::defined(name) for
+	the options that take filename.
+	* src/MultiUrlRequestInfo.cc
+	* src/Option.cc
+	* src/Option.h
+	* src/main.cc
+	* src/option_processing.cc
+	* test/OptionTest.cc
+
 2008-12-04  Tatsuhiro Tsujikawa  <t-tujikawa@users.sourceforge.net>
 
 	Documented the default value of --check-certificate option in man
diff --git a/src/MultiUrlRequestInfo.cc b/src/MultiUrlRequestInfo.cc
index 73684514..ddd1a87e 100644
--- a/src/MultiUrlRequestInfo.cc
+++ b/src/MultiUrlRequestInfo.cc
@@ -107,7 +107,7 @@ int MultiUrlRequestInfo::execute()
       DownloadEngineFactory().newDownloadEngine(_option, _requestGroups);
 
     try {
-      if(_option->defined(PREF_LOAD_COOKIES)) {
+      if(!_option->blank(PREF_LOAD_COOKIES)) {
 	File cookieFile(_option->get(PREF_LOAD_COOKIES));
 	if(cookieFile.isFile()) {
 	  e->getCookieStorage()->load(_option->get(PREF_LOAD_COOKIES));
@@ -138,12 +138,12 @@ int MultiUrlRequestInfo::execute()
 
 #ifdef ENABLE_SSL
     SharedHandle<TLSContext> tlsContext(new TLSContext());
-    if(_option->defined(PREF_CERTIFICATE) &&
-       _option->defined(PREF_PRIVATE_KEY)) {
+    if(!_option->blank(PREF_CERTIFICATE) &&
+       !_option->blank(PREF_PRIVATE_KEY)) {
       tlsContext->addClientKeyFile(_option->get(PREF_CERTIFICATE),
 				   _option->get(PREF_PRIVATE_KEY));
     }
-    if(_option->defined(PREF_CA_CERTIFICATE)) {
+    if(!_option->blank(PREF_CA_CERTIFICATE)) {
       try {
 	tlsContext->addTrustedCACertFile(_option->get(PREF_CA_CERTIFICATE));
       } catch(RecoverableException& e) {
diff --git a/src/Option.cc b/src/Option.cc
index a2d34e6d..b464ec50 100644
--- a/src/Option.cc
+++ b/src/Option.cc
@@ -48,10 +48,17 @@ void Option::put(const std::string& name, const std::string& value) {
   table[name] = value;
 }
 
-bool Option::defined(const std::string& name) const {
+bool Option::defined(const std::string& name) const
+{
   return table.count(name) == 1;
 }
 
+bool Option::blank(const std::string& name) const
+{
+  std::map<std::string, std::string>::const_iterator i = table.find(name);
+  return i == table.end() || (*i).second.empty();
+}
+
 const std::string& Option::get(const std::string& name) const {
   std::map<std::string, std::string>::const_iterator itr = table.find(name);
   if(itr == table.end()) {
diff --git a/src/Option.h b/src/Option.h
index e7e380a5..13818982 100644
--- a/src/Option.h
+++ b/src/Option.h
@@ -49,7 +49,12 @@ public:
   ~Option();
 
   void put(const std::string& name, const std::string& value);
+  // Returns true if name is defined. Otherwise returns false.
+  // Note that even if the value is a empty string, this method returns true.
   bool defined(const std::string& name) const;
+  // Returns true if name is not defined or the value is a empty string.
+  // Otherwise returns false.
+  bool blank(const std::string& name) const;
   const std::string& get(const std::string& name) const;
   int32_t getAsInt(const std::string& name) const;
   int64_t getAsLLInt(const std::string& name) const;
diff --git a/src/main.cc b/src/main.cc
index 26405810..714db62d 100644
--- a/src/main.cc
+++ b/src/main.cc
@@ -141,7 +141,7 @@ int main(int argc, char* argv[])
     int32_t returnValue = 0;
     std::deque<SharedHandle<RequestGroup> > requestGroups;
 #ifdef ENABLE_BITTORRENT
-    if(op->defined(PREF_TORRENT_FILE)) {
+    if(!op->blank(PREF_TORRENT_FILE)) {
       if(op->get(PREF_SHOW_FILES) == V_TRUE) {
 	DefaultBtContextHandle btContext(new DefaultBtContext());
 	btContext->load(op->get(PREF_TORRENT_FILE));
@@ -154,7 +154,7 @@ int main(int argc, char* argv[])
     else
 #endif // ENABLE_BITTORRENT
 #ifdef ENABLE_METALINK
-      if(op->defined(PREF_METALINK_FILE)) {
+      if(!op->blank(PREF_METALINK_FILE)) {
 	if(op->get(PREF_SHOW_FILES) == V_TRUE) {
 	  std::deque<SharedHandle<MetalinkEntry> > metalinkEntries;
 	  MetalinkHelper::parseAndQuery(metalinkEntries,
@@ -169,7 +169,7 @@ int main(int argc, char* argv[])
       }
       else
 #endif // ENABLE_METALINK
-	if(op->defined(PREF_INPUT_FILE)) {
+	if(!op->blank(PREF_INPUT_FILE)) {
 	  createRequestGroupForUriList(requestGroups, op);
 	} else {
 	  createRequestGroupForUri(requestGroups, op, args);
diff --git a/src/option_processing.cc b/src/option_processing.cc
index 169806a8..523658a3 100644
--- a/src/option_processing.cc
+++ b/src/option_processing.cc
@@ -617,12 +617,12 @@ Option* option_processing(int argc, char* const argv[])
   }
   if(
 #ifdef ENABLE_BITTORRENT
-     !op->defined(PREF_TORRENT_FILE) &&
+     op->blank(PREF_TORRENT_FILE) &&
 #endif // ENABLE_BITTORRENT
 #ifdef ENABLE_METALINK
-     !op->defined(PREF_METALINK_FILE) &&
+     op->blank(PREF_METALINK_FILE) &&
 #endif // ENABLE_METALINK
-     !op->defined(PREF_INPUT_FILE)) {
+     op->blank(PREF_INPUT_FILE)) {
     if(optind == argc) {
       std::cerr << MSG_URI_REQUIRED << std::endl;
       showUsage(TAG_HELP, oparser);
diff --git a/test/OptionTest.cc b/test/OptionTest.cc
index c219103a..306505a8 100644
--- a/test/OptionTest.cc
+++ b/test/OptionTest.cc
@@ -10,6 +10,8 @@ class OptionTest:public CppUnit::TestFixture {
   CPPUNIT_TEST(testPutAndGet);
   CPPUNIT_TEST(testPutAndGetAsInt);
   CPPUNIT_TEST(testPutAndGetAsDouble);
+  CPPUNIT_TEST(testDefined);
+  CPPUNIT_TEST(testBlank);
   CPPUNIT_TEST_SUITE_END();
 private:
 
@@ -20,6 +22,8 @@ public:
   void testPutAndGet();
   void testPutAndGetAsInt();
   void testPutAndGetAsDouble();
+  void testDefined();
+  void testBlank();
 };
 
 
@@ -48,4 +52,24 @@ void OptionTest::testPutAndGetAsDouble() {
   CPPUNIT_ASSERT_EQUAL(10.0, op.getAsDouble("key"));
 }
 
+void OptionTest::testDefined()
+{
+  Option op;
+  op.put("k", "v");
+  op.put("k1", "");
+  CPPUNIT_ASSERT(op.defined("k"));
+  CPPUNIT_ASSERT(op.defined("k1"));
+  CPPUNIT_ASSERT(!op.defined("undefined"));
+}
+
+void OptionTest::testBlank()
+{
+  Option op;
+  op.put("k", "v");
+  op.put("k1", "");
+  CPPUNIT_ASSERT(!op.blank("k"));
+  CPPUNIT_ASSERT(op.blank("k1"));
+  CPPUNIT_ASSERT(op.blank("undefined"));
+}
+
 } // namespace aria2