Include empty lines condition in PromptStipper and cell_magic.

IPython/core/inputtransformer2.py

@@ -61,6 +61,8 b' class PromptStripper:'
         return [self.prompt_re.sub('', l, count=1) for l in lines]
 
     def __call__(self, lines):
+        if not lines:
+            return lines
         if self.initial_re.match(lines[0]) or \
                 (len(lines) > 1 and self.prompt_re.match(lines[1])):
             return self._strip(lines)
@@ -74,7 +76,7 b' classic_prompt = PromptStripper('
 ipython_prompt = PromptStripper(re.compile(r'^(In \[\d+\]: |\s*\.{3,}: ?)'))
 
 def cell_magic(lines):
-    if not lines[0].startswith('%%'):
+    if not lines or not lines[0].startswith('%%'):
         return lines
     if re.match('%%\w+\?', lines[0]):
         # This case will be handled by help_end