From 13686776b902056e6898db0036535612e58755a6 Mon Sep 17 00:00:00 2001
From: Gustav Larsson <gustav.m.larsson@gmail.com>
Date: Wed, 30 Jul 2014 18:25:42 -0500
Subject: [PATCH] Fixes syntax error in older versions of graphviz.

Older versions of graphviz (tested on version 2.26.3 (20100126.1600))
complains when an attribute is empty without quotes. [label=] fails but
[label=""] works, so the quote_if_necessary function has been updated to
accommodate this.
---
 pydot/__init__.py | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/pydot/__init__.py b/pydot/__init__.py
index 142b039..ed8d1de 100644
--- a/pydot/__init__.py
+++ b/pydot/__init__.py
@@ -257,6 +257,10 @@ def needs_quotes(s):
 
 
 def quote_if_necessary(s):
+    # Older versions of graphviz throws a syntax error for empty values without
+    # quotes, e.g. [label=]
+    if s == '':
+        return '""'
 
     if isinstance(s, bool):
         if s is True: