Parse a subgraph event that has a struct

Questions & Feedback Questions
1 
Subgraph error 1/1, code: SubgraphSyncingFailure, error: Mapping aborted at generated/schema.ts, line 212, column 12, with message: unexpected null wasm backtrace

generated/schema.ts, line 212

210  get subdata(): Array<string> {
211   let value = this.get("subdata");
212   return value!.toStringArray();
213  }

contract.sol

    event Hello(address indexed owner, Data data);

    struct Subdata {
        string one;
        string two;
    }

    struct Data {
        string name;
        Subdata[] subdata;
    }

subgraph.yaml

      eventHandlers:
        - event: Hello(indexed address,(string,(string,string)[]))
          handler: handleHello

How to in mapping.ts get data and subdata struct?

event.params.data.subdata have error.

3

Solved a problem.

I added the ID to the automatic field.
Because of this there was an error.

type Data @entity {
  id: ID!
  subdata: [Subdata!] @derivedFrom(field: "data")
}

data.subdata.push(id) // error