changed macro to ignore empty trees and made compiler do the substitution work

hy/compiler.py

@@ -1421,6 +1421,8 @@ class HyASTCompiler(object):
 
     @builds(HyExpression)
     def compile_expression(self, expression):
+        if expression == []:
+            return self.compile_list(expression)
         fn = expression[0]
         func = None
         if isinstance(fn, HyKeyword):

hy/macros.py

@@ -71,10 +71,7 @@ _wrappers = {
 def process(tree, module_name):
     if isinstance(tree, HyExpression):
         if tree == []:
-            # set value to []
-            ntree = HyList()
-            ntree.replace(tree)
-            return ntree
+            return tree
         
         fn = tree[0]
         if fn in ("quote", "quasiquote"):