### Elasticsearch Version

8.1.1

### Installed Plugins

_No response_

### Java Version

_bundled_

###  OS Version

Darwin Kernel Version 21.4.0

### Problem Description

Under certain conditions, executing a range enrich policy on a field with wrong datatype gives a NPE instead of a more comprehensible error.

### Steps to Reproduce

```
PUT enrich_index
{
  "mappings": {
    "properties": {
      "object": {
        "properties": {
          "field": {
            "type": "keyword"
          }
        }
      }
    }
  }
}

PUT /_enrich/policy/enrich_policy
{
  "range": {
    "indices": "enrich_index",
    "match_field": "object",
    "enrich_fields": ["enrich_field"]
  }
}

POST /_enrich/policy/enrich_policy/_execute
```

Executing the policy returns:
```json
{
  "error" : {
    "root_cause" : [
      {
        "type" : "null_pointer_exception",
        "reason" : "Cannot invoke \"String.hashCode()\" because \"<local7>\" is null"
      }
    ],
    "type" : "null_pointer_exception",
    "reason" : "Cannot invoke \"String.hashCode()\" because \"<local7>\" is null"
  },
  "status" : 500
}
```

Interestingly enough, if the enrich index were created like this (without subfield in `object`):
```
PUT enrich_index
{
  "mappings": {
    "properties": {
      "object": {
        "properties": {
        }
      }
    }
  }
}
```
 

Executing the policy would return a much better error:
```json
{
  "error" : {
    "root_cause" : [
      {
        "type" : "exception",
        "reason" : "Field 'object' has type [object] which doesn't appear to be a range type"
      }
    ],
    "type" : "exception",
    "reason" : "Field 'object' has type [object] which doesn't appear to be a range type"
  },
  "status" : 500
}
```



### Logs (if relevant)

_No response_
x-pack/plugin/enrich/src/main/java/org/elasticsearch/xpack/enrich/EnrichPolicyRunner.java
*/
    private Client enrichOriginClient() {
        return new OriginSettingClient(client, ENRICH_ORIGIN);
    }
    private static Client wrapClient(Client in, String policyName, ExecuteEnrichPolicyTask task, ClusterService clusterService) {
        
        
        
        
        return new FilterClient(in) {
            @Override
            protected <Request extends ActionRequest, Response extends ActionResponse> void doExecute(
                ActionType<Response> action,
                Request request,
                ActionListener<Response> listener
            ) {
                String requestStep = request.getClass().getSimpleName();
                task.setStep(requestStep);
                if (task.isCancelled()) {
                    String message = "cancelled policy execution [" + policyName + "], status [" + Strings.toString(task.getStatus()) + "]";
                    listener.onFailure(new TaskCancelledException(message));
                    return;
                }
                request.setParentTask(clusterService.localNode().getId(), task.getId());
                super.doExecute(action, request, listener);
            }
        };
    }
}