### 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
"Policy [{}]: bulk index failed for index [{}], id [{}]",
                                    policyName,
                                    failure.getIndex(),
                                    failure.getId()
                                ),
                                failure.getCause()
                            );
                        }
                    }
                    delegate.onFailure(new ElasticsearchException("Encountered bulk failures during reindex process"));
                } else if (bulkByScrollResponse.getSearchFailures().size() > 0) {
                    logger.warn(
                        "Policy [{}]: encountered [{}] search failures. Turn on DEBUG logging for details.",
                        policyName,
                        bulkByScrollResponse.getSearchFailures().size()
                    );
                    if (logger.isDebugEnabled()) {
                        for (ScrollableHitSource.SearchFailure failure : bulkByScrollResponse.getSearchFailures()) {
                            logger.debug(
                                new ParameterizedMessage(
                                    "Policy [{}]: search failed for index [{}], shard [{}] on node [{}]",
                                    policyName,
                                    failure.getIndex(),
                                    failure.getShardId(),
                                    failure.getNodeId()
                                ),
                                failure.getReason()
                            );
                        }
                    }