[yang]Static route CLI command adds empty nexthop-vrf which results in yang validation failure

[dgsudharsan]

Description

When configuring static route through CLI, if nexthop-vrf is not configured, an empty string is set as value

https://github.com/sonic-net/sonic-utilities/blob/7100f73b107b5a7806488311e224e6be29c6b412/config/main.py#L7032

However the yang validation mandates nexthop-vrf to be a valid vrf string as per the pattern.

sonic-buildimage/src/sonic-yang-models/yang-models/sonic-static-route.yang

Line 114 in 4317df5

pattern "(((Vrf[a-zA-Z0-9_-]+)|(default)|(mgmt)),)*((Vrf[a-zA-Z0-9_-]+)|(default)|(mgmt))";

Hence when we config static route through CLI, save and perform config reload, it results in yang validation failure

  "STATIC_ROUTE|default|50.0.0.0/24": {
    "expireat": 1736209448.6722484,
    "ttl": -0.001,
    "type": "hash",
    "value": {
      "blackhole": "false",
      "distance": "0",
      "ifname": "",
      "nexthop": "20.0.0.2",
      "nexthop-vrf": ""
    }
  },

2025 Jan  7 02:20:27.950607 r-anaconda-51 INFO database.sh[4827]: libyang[0]: Value "" does not satisfy the constraint "(((Vrf[a-zA-Z0-9_-]+)|(default)|(mgmt)),)*((Vrf[a-zA-Z0-9_-]+)|(default)|(mgmt))" (range, length, or pattern). (path: /sonic-static-route:sonic-static-route/STATIC_ROUTE/STATIC_ROUTE_LIST[vrf_name='default'][prefix='50.0.0.0/24']/nexthop-vrf)
2025 Jan  7 02:20:27.951583 r-anaconda-51 ERR sonic_yang: Data Loading Failed:Value "" does not satisfy the constraint "(((Vrf[a-zA-Z0-9_-]+)|(default)|(mgmt)),)*((Vrf[a-zA-Z0-9_-]+)|(default)|(mgmt))" (range, length, or pattern).
2025 Jan  7 02:20:27.951682 r-anaconda-51 ERR config_validator.py: Yang validation failed: Data Loading Failed#012Value "" does not satisfy the constraint "(((Vrf[a-zA-Z0-9_-]+)|(default)|(mgmt)),)*((Vrf[a-zA-Z0-9_-]+)|(default)|(mgmt))" (range, length, or pattern).
2025 Jan  7 02:20:27.951759 r-anaconda-51 INFO database.sh[4827]: sonic_yang(3):Data Loading Failed:Value "" does not satisfy the constraint "(((Vrf[a-zA-Z0-9_-]+)|(default)|(mgmt)),)*((Vrf[a-zA-Z0-9_-]+)|(default)|(mgmt))" (range, length, or pattern).
2025 Jan  7 02:20:27.951805 r-anaconda-51 INFO database.sh[4827]: Traceback (most recent call last):
2025 Jan  7 02:20:27.951842 r-anaconda-51 INFO database.sh[4827]:   File "/usr/local/lib/python3.11/dist-packages/sonic_yang_ext.py", line 1176, in loadData
2025 Jan  7 02:20:27.954680 r-anaconda-51 INFO database.sh[4827]:     self.root = self.ctx.parse_data_mem(dumps(self.xlateJson), \
2025 Jan  7 02:20:27.954754 r-anaconda-51 INFO database.sh[4827]:                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2025 Jan  7 02:20:27.954781 r-anaconda-51 INFO database.sh[4827]:   File "/usr/lib/python3/dist-packages/yang.py", line 2574, in parse_data_mem
2025 Jan  7 02:20:27.956987 r-anaconda-51 INFO database.sh[4827]:     return _yang.Context_parse_data_mem(self, data, format, options)
2025 Jan  7 02:20:27.957072 r-anaconda-51 INFO database.sh[4827]:            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2025 Jan  7 02:20:27.957100 r-anaconda-51 INFO database.sh[4827]: RuntimeError: Value "" does not satisfy the constraint "(((Vrf[a-zA-Z0-9_-]+)|(default)|(mgmt)),)*((Vrf[a-zA-Z0-9_-]+)|(default)|(mgmt))" (range, length, or pattern).
2025 Jan  7 02:20:27.957122 r-anaconda-51 INFO database.sh[4827]: During handling of the above exception, another exception occurred:
2025 Jan  7 02:20:27.957142 r-anaconda-51 INFO database.sh[4827]: Traceback (most recent call last):
2025 Jan  7 02:20:27.957162 r-anaconda-51 INFO database.sh[4827]:   File "/usr/local/bin/config_validator.py", line 44, in <module>
2025 Jan  7 02:20:27.957188 r-anaconda-51 INFO database.sh[4827]:     main()
2025 Jan  7 02:20:27.957218 r-anaconda-51 INFO database.sh[4827]:   File "/usr/local/bin/config_validator.py", line 33, in main
2025 Jan  7 02:20:27.957289 r-anaconda-51 INFO database.sh[4827]:     yang_parser.loadData(configdbJson=config)
2025 Jan  7 02:20:27.957319 r-anaconda-51 INFO database.sh[4827]:   File "/usr/local/lib/python3.11/dist-packages/sonic_yang_ext.py", line 1183, in loadData
2025 Jan  7 02:20:27.957542 r-anaconda-51 INFO database.sh[4827]:     raise SonicYangException("Data Loading Failed\n{}".format(str(e)))
2025 Jan  7 02:20:27.957587 r-anaconda-51 INFO database.sh[4827]: sonic_yang_ext.SonicYangException: Data Loading Failed
2025 Jan  7 02:20:27.957611 r-anaconda-51 INFO database.sh[4827]: Value "" does not satisfy the constraint "(((Vrf[a-zA-Z0-9_-]+)|(default)|(mgmt)),)*((Vrf[a-zA-Z0-9_-]+)|(default)|(mgmt))" (range, length, or pattern).

Steps to reproduce the issue:

1. config static route through CLI
2. config save
3. config reload

Describe the results you received:

Config reload fails in yang validation

Describe the results you expected:

config reload should not fail.

Output of show version:

(paste your output here)

Output of show techsupport:

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Additional information you deem important (e.g. issue happens only occasionally):