```
ROW a="b c d"
| DISSECT a "%{b} %{} %{d}"
```
returns

```
       a       |       b       |               |       d       
---------------+---------------+---------------+---------------
b c d          |b              |null           |d 
```

it should ignore the empty pattern instead, and only return `a, b, d`
x-pack/plugin/esql/src/main/java/org/elasticsearch/xpack/esql/parser/LogicalPlanBuilder.java
Source src = source(ctx);
        return child -> new MvExpand(src, child, new UnresolvedAttribute(src, identifier), new UnresolvedAttribute(src, identifier));
    }
    @Override
    public Map<String, Object> visitCommandOptions(EsqlBaseParser.CommandOptionsContext ctx) {
        if (ctx == null) {
            return Map.of();
        }
        Map<String, Object> result = new HashMap<>();
        for (EsqlBaseParser.CommandOptionContext option : ctx.commandOption()) {
            result.put(visitIdentifier(option.identifier()), expression(option.constant()).fold());
        }
        return result;
    }
    @Override
    public LogicalPlan visitRowCommand(EsqlBaseParser.RowCommandContext ctx) {
        return new Row(source(ctx), visitFields(ctx.fields()));
    }
    @Override
    public LogicalPlan visitFromCommand(EsqlBaseParser.FromCommandContext ctx) {
        Source source = source(ctx);
        TableIdentifier table = new TableIdentifier(source, null, visitSourceIdentifiers(ctx.sourceIdentifier()));
        Map<String, Attribute> metadataMap = new LinkedHashMap<>();
        if (ctx.metadata() != null) {
            for (var c : ctx.metadata().sourceIdentifier()) {
                String id = visitSourceIdentifier(c);
                Source src = source(c);
                if (MetadataAttribute.isSupported(id) == false) {
                    throw new ParsingException(src, "unsupported metadata field [" + id + "]");
                }