About the design of `Predicate` in `EdgeExpand`

In `EdgeExpand`, a predicate can possibly be given to filter unexpected results.
```json
{
"opr": {
"edge": {
"direction": "OUT",
"params": {
"tables": [
{
"id": 10
}
],
"columns": [
{
"name": "workFrom"
}
],
"isAllColumns": false,
"predicate": {
"operators": [
{
"var": {
"property": {
"key": {
"name": "workFrom"
}
},
"nodeType": {
"dataType": "INT32"
}
},
"nodeType": {
"dataType": "INT32"
}
},
{
"nodeType": {
"dataType": "BOOLEAN"
},
"logical": "LT"
},
{
"param": {
"name": "workFromYear",
"index": 2,
"dataType": {
"dataType": "INT32"
}
},
"nodeType": {
"dataType": "INT32"
}
}
]
},
"sampleRatio": 1,
"extra": {}
},
"expandOpt": "EDGE",
"isOptional": false,
"vTag": 1,
"alias": 2
}
}
}
```

The may be confusing point about this predicate:

The tag of the Variable is not given, so should I use the current visiting `edge` or the previous visited HEAD?