Lists built from function calls are not "literal".

4 files changed, 22 insertions, 3 deletions

diff --git a/scss/expression.py b/scss/expression.py
index 8b42e7d..0c889b1 100644
--- a/scss/expression.py
+++ b/scss/expression.py
@@ -1,4 +1,5 @@
 from __future__ import absolute_import
+from __future__ import print_function
 
 from functools import partial
 import logging
@@ -378,8 +379,17 @@ class ListLiteral(Expression):
 
     def evaluate(self, calculator, divide=False):
         items = [item.evaluate(calculator, divide=divide) for item in self.items]
-        # TODO sort of overloading "divide" here...  rename i think
-        return List(items, use_comma=self.comma, is_literal=not divide)
+
+        # Whether this is a "plain" literal matters for null removal: nulls are
+        # left alone if this is a completely vanilla CSS property
+        is_literal = True
+        if divide:
+            # TODO sort of overloading "divide" here...  rename i think
+            is_literal = False
+        elif not all(isinstance(item, Literal) for item in self.items):
+            is_literal = False
+
+        return List(items, use_comma=self.comma, is_literal=is_literal)
 
 
 class MapLiteral(Expression):
diff --git a/scss/tests/files/general/null-values.css b/scss/tests/files/general/null-values.css
index 16deaae..b3e9775 100644
--- a/scss/tests/files/general/null-values.css
+++ b/scss/tests/files/general/null-values.css
@@ -2,4 +2,5 @@ div {
   a: 1, 2, 3;
   b: 1, null, 2, null, 3;
   c: 1  2;
+  e: 1, 2, 3, ;
 }
diff --git a/scss/tests/files/general/null-values.scss b/scss/tests/files/general/null-values.scss
index d657ab2..f64fecb 100644
--- a/scss/tests/files/general/null-values.scss
+++ b/scss/tests/files/general/null-values.scss
@@ -8,4 +8,6 @@ div {
     c: 1 (null, null) 2;
     // empty properties aren't printed
     d: (null, null);
+    // and it applies recursively
+    e: (((null, 1, null), (null, 2), null), (3, null, (null, null)));
 }
diff --git a/scss/types.py b/scss/types.py
index 4a027d7..aafbab4 100644
--- a/scss/types.py
+++ b/scss/types.py
@@ -685,7 +685,13 @@ class List(Value):
             max_list, min_list = (self, other) if len(self) > len(other) else (other, self)
             return List([item + max_list[i] for i, item in enumerate(min_list)], use_comma=self.use_comma)
 
-        return List([item + other for item in self], use_comma=self.use_comma)
+        elif isinstance(other, String):
+            # UN-DEVIATION: adding a string should fall back to canonical
+            # behavior of string addition
+            return super(List, self).__add__(other)
+
+        else:
+            return List([item + other for item in self], use_comma=self.use_comma)
 
     def __sub__(self, other):
         if isinstance(other, List):