### 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
new SearchRequest(".enrich-test1").source(
                SearchSourceBuilder.searchSource().query(QueryBuilders.matchQuery("data.subnet", "10.0.0.1"))
            )
        ).actionGet();
        assertThat(enrichSearchResponse.getHits().getTotalHits().value, equalTo(1L));
        Map<String, Object> enrichDocument = enrichSearchResponse.getHits().iterator().next().getSourceAsMap();
        assertNotNull(enrichDocument);
        assertThat(enrichDocument.size(), is(equalTo(1)));
        Map<?, ?> resultDataField = ((Map<?, ?>) enrichDocument.get("data"));
        assertNotNull(resultDataField);
        assertThat(resultDataField.size(), is(equalTo(2)));
        assertThat(resultDataField.get("subnet"), is(equalTo("10.0.0.0/8")));
        assertThat(resultDataField.get("department"), is(equalTo("research")));
        assertNull(resultDataField.get("field3"));
        
        validateSegments(createdEnrichIndex, 1);
        
        ensureEnrichIndexIsReadOnly(createdEnrichIndex);
    }
    public void testRunnerTwoObjectLevelsSourceMapping() throws Exception {
        final String sourceIndex = "source-index";
        XContentBuilder mappingBuilder = JsonXContent.contentBuilder();
        mappingBuilder.startObject()
            .startObject(MapperService.SINGLE_MAPPING_NAME)
            .startObject("properties")
            .startObject("data")
            .startObject("properties")
            .startObject("fields")
            .startObject("properties")
            .startObject("field1")