raise exception for invalid param syntax

sanic/router.py

@@ -93,6 +93,8 @@ class Router:
         pattern = 'string'
         if ':' in parameter_string:
             name, pattern = parameter_string.split(':', 1)
+            if not name:
+                raise ValueError("Invalid parameter syntax: {}".format(parameter_string))
 
         default = (str, pattern)
         # Pull from pre-configured types

tests/test_routes.py

@@ -71,6 +71,16 @@ def test_route_strict_slash():
     request, response = app.test_client.post('/post')
     assert response.status == 404
 
+def test_route_invalid_parameter_syntax():
+    with pytest.raises(ValueError):
+        app = Sanic('test_route_invalid_param_syntax')
+
+        @app.get('/get/<:string>', strict_slashes=True)
+        def handler(request):
+            return text('OK')
+
+        request, response = app.test_client.get('/get')
+
 def test_route_strict_slash_default_value():
     app = Sanic('test_route_strict_slash', strict_slashes=True)