Return a sensible error when the parameter is not found

moto/ssm/responses.py

@@ -145,6 +145,13 @@ class SimpleSystemManagerResponse(BaseResponse):
 
         result = self.ssm_backend.get_parameter_history(name, with_decryption)
 
+        if result is None:
+            error = {
+                "__type": "ParameterNotFound",
+                "message": "Parameter {0} not found.".format(name),
+            }
+            return json.dumps(error), dict(status=400)
+
         response = {"Parameters": []}
         for parameter_version in result:
             param_data = parameter_version.describe_response_object(

tests/test_ssm/test_ssm_boto3.py

@@ -879,6 +879,20 @@ def test_get_parameter_history_with_secure_string():
         len(parameters_response).should.equal(3)
 
 
+@mock_ssm
+def test_get_parameter_history_missing_parameter():
+    client = boto3.client("ssm", region_name="us-east-1")
+
+    try:
+        client.get_parameter_history(Name="test_noexist")
+        raise RuntimeError("Should have failed")
+    except botocore.exceptions.ClientError as err:
+        err.operation_name.should.equal("GetParameterHistory")
+        err.response["Error"]["Message"].should.equal(
+            "Parameter test_noexist not found."
+        )
+
+
 @mock_ssm
 def test_add_remove_list_tags_for_resource():
     client = boto3.client("ssm", region_name="us-east-1")