Make error statements in parameters.step more informative

Signed-off-by: Yuki Iwai <[email protected]>

Author: tenzen-y

pkg/suggestion/v1beta1/internal/search_space.py

@@ -49,7 +49,10 @@ def convert_to_combinations(search_space):
                 combinations[parameter.name] = range(int(parameter.min), int(parameter.max)+1, int(parameter.step))
             elif parameter.type == DOUBLE:
                 if parameter.step == "" or parameter.step is None:
-                    raise Exception("Param {} step is nil".format(parameter.name))
+                    raise Exception(
+                        "Param {} step is nil; For discrete search space, all parameters must include step".
+                        format(parameter.name)
+                    )
                 double_list = np.arange(float(parameter.min), float(parameter.max)+float(parameter.step),
                                         float(parameter.step))
                 if double_list[-1] > float(parameter.max):