From a981f560b6bd1f6e2f67a230e6a0ff8b4fc0d66f Mon Sep 17 00:00:00 2001
From: Mickey Rose <mickey.rose@seznam.cz>
Date: Tue, 15 Mar 2016 00:29:17 +0100
Subject: [PATCH] fix empty string value::to_expresssion_string

---
 src/value.cpp | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/value.cpp b/src/value.cpp
index efcd15b5f..a3c8770cc 100644
--- a/src/value.cpp
+++ b/src/value.cpp
@@ -761,6 +761,13 @@ struct to_expression_string_impl
 
     std::string operator()(value_unicode_string const& val) const
     {
+        // toUTF8(sink) doesn't Flush() the sink if the source string
+        // is empty -- we must return a pair of quotes in that case
+        //  https://github.com/mapnik/mapnik/issues/3362
+        if (val.isEmpty())
+        {
+            return std::string(2, quote_);
+        }
         EscapingByteSink sink(quote_);
         val.toUTF8(sink);
         return sink.dest_;