From 564af5a65cc607c26db926032e927ea5abb0a5ae Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Fri, 22 Jan 2016 19:27:33 +0100
Subject: [PATCH] [otlLib] Return None if coverage is empty

---
 Lib/fontTools/otlLib/builder.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/Lib/fontTools/otlLib/builder.py b/Lib/fontTools/otlLib/builder.py
index d1279d91f..43ada7173 100644
--- a/Lib/fontTools/otlLib/builder.py
+++ b/Lib/fontTools/otlLib/builder.py
@@ -5,6 +5,8 @@ from fontTools.ttLib.tables.otBase import ValueRecord, valueRecordFormatDict
 
 
 def buildCoverage(glyphs, glyphMap):
+    if not glyphs:
+        return None
     self = ot.Coverage()
     self.glyphs = sorted(glyphs, key=glyphMap.__getitem__)
     return self