[yang] Fix yang validation failure when table contains empty value (#10431)

Why I did it
Fix #9746

How I did it
Split the check condition based on non-exist and zero length.

How to verify it
Run verification script when table contains empty value

src/sonic-yang-mgmt/sonic_yang_ext.py

@@ -591,18 +591,23 @@ class SonicYangExtMixin:
     """
     def _xlateContainerInContainer(self, model, yang, configC, table):
         ccontainer = model
-        #print(ccontainer['@name'])
-        yang[ccontainer['@name']] = dict()
-        if not configC.get(ccontainer['@name']):
+        ccName = ccontainer['@name']
+        yang[ccName] = dict()
+        if ccName not in configC:
+            # Inner container doesn't exist in config
             return
-        self.sysLog(msg="xlateProcessListOfContainer: {}".format(ccontainer['@name']))
-        self._xlateContainer(ccontainer, yang[ccontainer['@name']], \
-        configC[ccontainer['@name']], table)
+        if len(configC[ccName]) == 0:
+            # Empty container, clean config and return
+            del configC[ccName]
+            return
+        self.sysLog(msg="xlateProcessListOfContainer: {}".format(ccName))
+        self._xlateContainer(ccontainer, yang[ccName], \
+        configC[ccName], table)
         # clean empty container
-        if len(yang[ccontainer['@name']]) == 0:
-            del yang[ccontainer['@name']]
+        if len(yang[ccName]) == 0:
+            del yang[ccName]
         # remove copy after processing
-        del configC[ccontainer['@name']]
+        del configC[ccName]
 
         return
 

src/sonic-yang-mgmt/tests/libyang-python-tests/test_sonic_yang.py

@@ -364,5 +364,20 @@ class Test_SonicYang(object):
 
         return
 
+    def test_special_json_with_yang(self, sonic_yang_data):
+        # in this test, we validate unusual json config and check if
+        # loadData works successfully
+        test_file = sonic_yang_data['test_file']
+        syc = sonic_yang_data['syc']
+
+        # read config
+        jIn = self.readIjsonInput(test_file, 'SAMPLE_CONFIG_DB_SPECIAL_CASE')
+        jIn = json.loads(jIn)
+
+        # load config and create Data tree
+        syc.loadData(jIn)
+
+        return
+
     def teardown_class(self):
         pass

src/sonic-yang-models/tests/files/sample_config_db.json

@@ -304,7 +304,7 @@
                 "switch_id": "2",
                 "switch_type": "voq",
                 "max_cores": "8",
-                "sub_role": "FrondEnd",
+                "sub_role": "FrontEnd",
                 "dhcp_server": "disabled"
             }
         },
@@ -1694,5 +1694,11 @@
         "UNKNOWN_TABLE": {
             "Error": "This Table is for testing, This Table does not have YANG models."
         }
+    },
+    "SAMPLE_CONFIG_DB_SPECIAL_CASE": {
+        "TACPLUS": {
+            "global": {
+            }
+        }
     }
 }

src/sonic-yang-models/yang-models/sonic-device_metadata.yang

@@ -129,7 +129,7 @@ module sonic-device_metadata {
 
                 leaf sub_role {
                     type string;
-                    description "sub_role indicates if ASIC is FrondEnd or BackEnd.";
+                    description "sub_role indicates if ASIC is FrontEnd or BackEnd.";
                 }
 
                 leaf downstream_subrole {