```
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/test/java/org/elasticsearch/xpack/esql/parser/StatementParserTests.java
import org.elasticsearch.xpack.ql.expression.NamedExpression;
import org.elasticsearch.xpack.ql.expression.Order;
import org.elasticsearch.xpack.ql.expression.ReferenceAttribute;
import org.elasticsearch.xpack.ql.expression.UnresolvedAttribute;
import org.elasticsearch.xpack.ql.expression.function.UnresolvedFunction;
import org.elasticsearch.xpack.ql.expression.predicate.logical.Not;
import org.elasticsearch.xpack.ql.expression.predicate.operator.comparison.BinaryComparison;
import org.elasticsearch.xpack.ql.plan.logical.Aggregate;
import org.elasticsearch.xpack.ql.plan.logical.Filter;
import org.elasticsearch.xpack.ql.plan.logical.Limit;
import org.elasticsearch.xpack.ql.plan.logical.LogicalPlan;
import org.elasticsearch.xpack.ql.plan.logical.OrderBy;
import org.elasticsearch.xpack.ql.type.DataType;
import org.elasticsearch.xpack.ql.type.DataTypes;
import org.elasticsearch.xpack.versionfield.Version;
import java.math.BigInteger;
import java.time.Duration;
import java.time.Period;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.function.Function;
import static org.elasticsearch.xpack.ql.expression.Literal.FALSE;
import static org.elasticsearch.xpack.ql.expression.Literal.TRUE;
import static org.elasticsearch.xpack.ql.expression.function.FunctionResolutionStrategy.DEFAULT;
import static org.elasticsearch.xpack.ql.tree.Source.EMPTY;
import static org.elasticsearch.xpack.ql.type.DataTypes.KEYWORD;
import static org.elasticsearch.xpack.ql.util.NumericUtils.asLongUnsigned;
import static org.hamcrest.Matchers.allOf;
import static org.hamcrest.Matchers.containsString;