Filter null values from the _concat() list. (Chad Austin)

2 files changed, 15 insertions, 11 deletions

diff --git a/src/CHANGES.txt b/src/CHANGES.txt
index bf2c760..b5ed500 100644
--- a/src/CHANGES.txt
+++ b/src/CHANGES.txt
@@ -22,6 +22,9 @@ RELEASE 0.96 - XXX
   - Allow the emitter argument to a Builder() to be or expand to a list
     of emitter functions, which will be called in sequence.
 
+  - Suppress null values in construction variables like $LIBS that use
+    the internal _concat() function.
+
   From Chad Austin and Christoph Wiedemann:
 
   - Add support for a $RPATH variable to supply a list of directories
diff --git a/src/engine/SCons/Defaults.py b/src/engine/SCons/Defaults.py
index 94ab8d5..89ac0d3 100644
--- a/src/engine/SCons/Defaults.py
+++ b/src/engine/SCons/Defaults.py
@@ -173,20 +173,21 @@ def _concat(prefix, list, suffix, env, f=lambda x: x):
 
     for x in list:
         x = str(x)
+        if x:
 
-        if prefix:
-            if prefix[-1] == ' ':
-                ret.append(prefix[:-1])
-            elif x[:len(prefix)] != prefix:
-                x = prefix + x
+            if prefix:
+                if prefix[-1] == ' ':
+                    ret.append(prefix[:-1])
+                elif x[:len(prefix)] != prefix:
+                    x = prefix + x
 
-        ret.append(x)
+            ret.append(x)
 
-        if suffix:
-            if suffix[0] == ' ':
-                ret.append(suffix[1:])
-            elif x[-len(suffix):] != suffix:
-                ret[-1] = ret[-1]+suffix
+            if suffix:
+                if suffix[0] == ' ':
+                    ret.append(suffix[1:])
+                elif x[-len(suffix):] != suffix:
+                    ret[-1] = ret[-1]+suffix
 
     return ret