From f20b4edc15c1fbfdb16feb07b6eae2b71a5af31f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?V=C3=ADt=20Ondruch?= <v.ondruch@tiscali.cz>
Date: Mon, 11 Mar 2013 17:33:19 +0100
Subject: [PATCH] Prevent failure when "prefix" is empty string.

In case that "prefix" is empty string, the config_string returns false. Default to empty string for that case.
---
 ext/RMagick/extconf.rb | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/ext/RMagick/extconf.rb b/ext/RMagick/extconf.rb
index d3228dd3e..f131a6e25 100644
--- a/ext/RMagick/extconf.rb
+++ b/ext/RMagick/extconf.rb
@@ -78,7 +78,7 @@ def check_multiple_imagemagick_versions()
 # binaries). This causes problems when /usr/lib is in the path (e.g., using
 # the default Ruby installation).
 def check_partial_imagemagick_versions()
-   prefix = config_string("prefix")
+   prefix = config_string("prefix") || ""
    matches = [
      prefix+"/lib/lib?agick*",
      prefix+"/include/ImageMagick",