Strip merge suffix in root node as well

Otherwise `key+` defined in root node or node with broken
inheritance will be called `key+` instead of `key`.
All other nodes already strip the merge suffix

Fix: #277

examples/merge/main.fmf

@@ -0,0 +1,3 @@
+# Merge suffix can be used and will be stripped
+environment+:
+    SOME: value

examples/merge/stray.fmf

@@ -0,0 +1,6 @@
+/:
+  inherit: false
+
+# Merge suffix will be stripped
+environment+:
+    NOTHING: here

fmf/base.py

@@ -372,17 +372,15 @@ def init(path):
 
     def merge(self, parent=None):
         """ Merge parent data """
-        # Check parent, append source files
+        # Check parent
         if parent is None:
             parent = self.parent
-        if parent is None:
-            return
-        # Do not inherit when disabled
-        if self._directives.get("inherit") is False:
-            return
-        self.sources = parent.sources + self.sources
-        # Merge child data with parent data
-        data = copy.deepcopy(parent.data)
+        if self._directives.get("inherit") is False or parent is None:
+            # Nothing to inherit
+            data = {}
+        else:
+            self.sources = parent.sources + self.sources
+            data = copy.deepcopy(parent.data)
         self._merge_special(data, self.data)
         self.data = data
 

tests/unit/test_base.py

@@ -174,6 +174,14 @@ def test_adjust_can_extend(self):
         assert child.data['environment']['FOO'] == "bar"
         assert child.data['environment']['BAR'] == "baz"
 
+    def test_node_without_parent_strips_merge_suffix(self):
+        """ Merge suffix is stripped in the top node as well """
+        tree = Tree(EXAMPLES + 'merge')
+        stray_child = tree.find('/stray')
+        assert 'environment' in stray_child.data
+        child = tree.find('/parent/reduced')
+        assert 'environment' in child.data
+
     def test_deep_hierarchy(self):
         """ Deep hierarchy on one line """
         deep = Tree(EXAMPLES + "deep")