### Elasticsearch Version

8.3.0

### Installed Plugins

_No response_

### Java Version

_bundled_

### OS Version

arm64

### Problem Description

When using the `_terms_enum` API, if remote clusters return failures, but the local cluster doesn't, a null exception is thrown:

```
{
  "error": {
    "root_cause": [
      {
        "type": "null_pointer_exception",
        "reason": "Cannot invoke \"java.util.List.add(Object)\" because \"shardFailures\" is null"
      }
    ],
    "type": "null_pointer_exception",
    "reason": "Cannot invoke \"java.util.List.add(Object)\" because \"shardFailures\" is null"
  },
  "status": 500
}
```

### Steps to Reproduce

Call the _terms_enum API with a remote cluster that will return failures, e.g. because of this bug: https://github.com/elastic/elasticsearch/issues/86187

### Logs (if relevant)

_No response_
x-pack/plugin/mapper-constant-keyword/src/main/java/org/elasticsearch/xpack/constantkeyword/mapper/ConstantKeywordFieldMapper.java
if (value == null) {
                return false;
            }
            return Regex.simpleMatch(pattern, value, caseInsensitive);
        }
        @Override
        public Query existsQuery(SearchExecutionContext context) {
            return value != null ? new MatchAllDocsQuery() : new MatchNoDocsQuery();
        }
        @Override
        public Query rangeQuery(
            Object lowerTerm,
            Object upperTerm,
            boolean includeLower,
            boolean includeUpper,
            ShapeRelation relation,
            ZoneId timeZone,
            DateMathParser parser,
            SearchExecutionContext context
        ) {
            if (this.value == null) {
                return new MatchNoDocsQuery();
            }
            final BytesRef valueAsBytesRef = new BytesRef(value);
            if (lowerTerm != null && BytesRefs.toBytesRef(lowerTerm).compareTo(valueAsBytesRef) >= (includeLower ? 1 : 0)) {
                return new MatchNoDocsQuery();
            }
            if (upperTerm != null && valueAsBytesRef.compareTo(BytesRefs.toBytesRef(upperTerm)) >= (includeUpper ? 1 : 0)) {
                return new MatchNoDocsQuery();
            }