clearer lexicon error messages

libwccl/lexicon/lexicon.cpp

@@ -33,13 +33,13 @@ boost::shared_ptr<StrSet> Lexicon::translate(const StrSet& set) const
 void Lexicon::insert(const UnicodeString& key, const UnicodeString& value)
 {
 	if (has_key(key)) {
-		throw InvalidArgument("key", PwrNlp::to_utf8(key) + " - entry already added.");
+		throw InvalidArgument("key", "Duplicated key in lexicon: " + PwrNlp::to_utf8(key));
 	}
 	if (key.isEmpty()) {
-		throw InvalidArgument("key", "Cannot add an empty string.");
+		throw InvalidArgument("key", "Empty key string in lexicon.");
 	}
 	if (value.isEmpty()) {
-		throw InvalidArgument("value", "Cannot add an empty string.");
+		throw InvalidArgument("value", "Empty value string in lexicon.");
 	}
 	map_[key] = value;
 }