Empty Range Bound Specified for Partition

Dear Professionals,
Just i have installed "PostgreSQL 11.1". And i
have started to create partitions. I've created RANGE partition table as
like below.

pgsql> create table test_parent_partition(
item_id integer,
item_name character varying,
item_qty character varying)
partition by range(item_qty);

pgsql> create table test_upto_50 partition of test_parent_partition
for values from ('0') to ('50');

Above 1st partition table was created. After that i have taken next step to
create another partition talbe. But while am creating another partition
table like below query.

pgsql> create table test_upto_100 partition of test_parent_partition
for values from ('51') to ('100');

It was showing error like this..

ERROR: empty range bound specified for partition "test_upto_100" DETAIL:
Specified lower bound ('51') is greater than or equal to upper bound
('100'). SQL state: 42P17

I am not getting, please give me cause of this and solution.

--
*Thanks & Best Regards:*
Ramanna Gunde

*Don't complain about the HEAT,*

*PLANT A .*