Fix TypeError if no input_parameters added

By calling solution.add_action with no input_parameters, TypeError:
'NoneType' object does not support item assignment was occurred.
This patch fix it.

Change-Id: Ia2ad0c18bc20468ca73c0ab70495fac2c90e0640
Closes-Bug: #1647927

watcher/decision_engine/solution/default.py

@@ -41,6 +41,9 @@ class DefaultSolution(base.BaseSolution):
             if baction.BaseAction.RESOURCE_ID in input_parameters.keys():
                 raise exception.ReservedWord(name=baction.BaseAction.
                                              RESOURCE_ID)
+        else:
+            input_parameters = {}
+
         if resource_id is not None:
             input_parameters[baction.BaseAction.RESOURCE_ID] = resource_id
         action = {

watcher/tests/decision_engine/solution/test_default_solution.py

@@ -43,3 +43,18 @@ class TestDefaultSolution(base.TestCase):
                          solution.actions[0].get('action_type'))
         self.assertEqual(expected_parameters,
                          solution.actions[0].get('input_parameters'))
+
+    def test_default_solution_with_no_input_parameters(self):
+        solution = default.DefaultSolution(
+            goal=mock.Mock(), strategy=mock.Mock())
+        solution.add_action(action_type="nop",
+                            resource_id="b199db0c-1408-4d52-b5a5-5ca14de0ff36")
+        self.assertEqual(1, len(solution.actions))
+        expected_action_type = "nop"
+        expected_parameters = {
+            "resource_id": "b199db0c-1408-4d52-b5a5-5ca14de0ff36"
+        }
+        self.assertEqual(expected_action_type,
+                         solution.actions[0].get('action_type'))
+        self.assertEqual(expected_parameters,
+                         solution.actions[0].get('input_parameters'))