### 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
String createdEnrichIndex = ".enrich-test1-" + createTime;
        GetIndexResponse enrichIndex = getGetIndexResponseAndCheck(createdEnrichIndex);
        
        Map<String, Object> mapping = enrichIndex.getMappings().get(createdEnrichIndex).sourceAsMap();
        validateMappingMetadata(mapping, policyName, policy);
        assertThat(mapping.get("dynamic"), is("false"));
        Map<?, ?> properties = (Map<?, ?>) mapping.get("properties");
        assertNotNull(properties);
        assertThat(properties.size(), is(equalTo(1)));
        Map<?, ?> field1 = (Map<?, ?>) properties.get("field1");
        assertNotNull(field1);
        assertThat(field1.get("type"), is(equalTo("keyword")));
        assertThat(field1.get("doc_values"), is(false));
        
        SearchResponse enrichSearchResponse = client().search(
            new SearchRequest(".enrich-test1").source(SearchSourceBuilder.searchSource().query(QueryBuilders.matchAllQuery()))
        ).actionGet();
        assertThat(enrichSearchResponse.getHits().getTotalHits().value, equalTo(1L));
        Map<String, Object> enrichDocument = enrichSearchResponse.getHits().iterator().next().getSourceAsMap();
        assertNotNull(enrichDocument);
        assertThat(enrichDocument.size(), is(equalTo(3)));
        assertThat(enrichDocument.get("field1"), is(equalTo("value1")));
        assertThat(enrichDocument.get("field2"), is(equalTo(2)));
        assertThat(enrichDocument.get("field5"), is(equalTo("value5")));
        
        validateSegments(createdEnrichIndex, 1);
        
        ensureEnrichIndexIsReadOnly(createdEnrichIndex);
    }
    public void testRunnerGeoMatchType() throws Exception {