```
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
public PlanFactory visitDropCommand(EsqlBaseParser.DropCommandContext ctx) {
        var identifiers = ctx.sourceIdentifier();
        List<NamedExpression> removals = new ArrayList<>(identifiers.size());
        for (EsqlBaseParser.SourceIdentifierContext idCtx : identifiers) {
            Source src = source(idCtx);
            String identifier = visitSourceIdentifier(idCtx);
            if (identifier.equals(WILDCARD)) {
                throw new ParsingException(src, "Removing all fields is not allowed [{}]", src.text());
            }
            removals.add(new UnresolvedAttribute(src, identifier));
        }
        return child -> new Drop(source(ctx), child, removals);
    }
    @Override
    public PlanFactory visitRenameCommand(EsqlBaseParser.RenameCommandContext ctx) {
        List<Alias> renamings = ctx.renameClause().stream().map(this::visitRenameClause).toList();
        return child -> new Rename(source(ctx), child, renamings);
    }
    @Override
    public PlanFactory visitKeepCommand(EsqlBaseParser.KeepCommandContext ctx) {
        if (ctx.PROJECT() != null) {
            addWarning("PROJECT command is no longer supported, please use KEEP instead");
        }
        List<NamedExpression> projections = new ArrayList<>(ctx.sourceIdentifier().size());
        boolean hasSeenStar = false;
        for (var srcIdCtx : ctx.sourceIdentifier()) {
            NamedExpression ne = visitProjectExpression(srcIdCtx);
            if (ne instanceof UnresolvedStar) {
                if (hasSeenStar) {
                    throw new ParsingException(ne.source(), "Cannot specify [*] more than once", ne.source().text());