share-group-type-unset unable to unset single property

[Vida Haririan]

Used the share-group-type-set command to set multiple sgt properties.
Command succeeded,

$ openstack share group type set default --group-specs 'key=12 snapshot_support=False'
+-------------+--------------------------------------+
| Field | Value |
+-------------+--------------------------------------+
| id | f5238905-ff83-429f-bd78-241fcd9a1f4f |
| name | default |
| share_types | f951a739-0200-45ec-9e43-6ab34d30a567 |
| visibility | public |
| is_default | True |
| group_specs | key : 12 snapshot_support=False |
+-------------+--------------------------------------+

Using the sgt unset command failed to remove selected sgt property.

$ openstack share group type unset default key
+-------------+--------------------------------------+
| Field | Value |
+-------------+--------------------------------------+
| id | f5238905-ff83-429f-bd78-241fcd9a1f4f |
| name | default |
| share_types | f951a739-0200-45ec-9e43-6ab34d30a567 |
| visibility | public |
| is_default | True |
| group_specs | |
+-------------+--------------------------------------+

Actual results: All set group-specs were unset
Expected results: Expected the snapshot_support=False to remain set.