### 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/test/java/org/elasticsearch/xpack/enrich/EnrichPolicyRunnerTests.java
import org.elasticsearch.action.admin.indices.refresh.RefreshAction;
import org.elasticsearch.action.admin.indices.segments.IndexSegments;
import org.elasticsearch.action.admin.indices.segments.IndexShardSegments;
import org.elasticsearch.action.admin.indices.segments.IndicesSegmentResponse;
import org.elasticsearch.action.admin.indices.segments.IndicesSegmentsAction;
import org.elasticsearch.action.admin.indices.segments.IndicesSegmentsRequest;
import org.elasticsearch.action.admin.indices.segments.ShardSegments;
import org.elasticsearch.action.admin.indices.settings.put.UpdateSettingsAction;
import org.elasticsearch.action.index.IndexRequest;
import org.elasticsearch.action.index.IndexResponse;
import org.elasticsearch.action.search.SearchRequest;
import org.elasticsearch.action.search.SearchResponse;
import org.elasticsearch.action.support.WriteRequest;
import org.elasticsearch.client.internal.Client;
import org.elasticsearch.client.internal.FilterClient;
import org.elasticsearch.cluster.metadata.IndexNameExpressionResolver;
import org.elasticsearch.cluster.service.ClusterService;
import org.elasticsearch.common.settings.Settings;
import org.elasticsearch.index.IndexNotFoundException;
import org.elasticsearch.index.engine.Segment;
import org.elasticsearch.index.mapper.MapperService;
import org.elasticsearch.index.query.QueryBuilders;
import org.elasticsearch.ingest.common.IngestCommonPlugin;
import org.elasticsearch.plugins.Plugin;
import org.elasticsearch.reindex.ReindexPlugin;
import org.elasticsearch.rest.RestStatus;
import org.elasticsearch.search.builder.SearchSourceBuilder;
import org.elasticsearch.tasks.Task;
import org.elasticsearch.tasks.TaskAwareRequest;
import org.elasticsearch.tasks.TaskId;