```
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
assertThat(comparison.left(), instanceOf(UnresolvedAttribute.class));
                assertThat(((UnresolvedAttribute) comparison.left()).name(), equalTo(expectedIdentifiers[j]));
                assertThat(comparison.right(), instanceOf(Literal.class));
                assertThat(((Literal) comparison.right()).value(), equalTo(123));
                assertThat(filter.child(), equalTo(PROCESSING_CMD_INPUT));
            }
        }
    }
    public void testBooleanLiteralCondition() {
        LogicalPlan where = processingCommand("where true");
        assertThat(where, instanceOf(Filter.class));
        Filter w = (Filter) where;
        assertThat(w.child(), equalTo(PROCESSING_CMD_INPUT));
        assertThat(w.condition(), equalTo(TRUE));
    }
    public void testBasicLimitCommand() {
        LogicalPlan plan = statement("from text | where true | limit 5");
        assertThat(plan, instanceOf(Limit.class));
        Limit limit = (Limit) plan;
        assertThat(limit.limit(), instanceOf(Literal.class));
        assertThat(((Literal) limit.limit()).value(), equalTo(5));
        assertThat(limit.children().size(), equalTo(1));
        assertThat(limit.children().get(0), instanceOf(Filter.class));
        assertThat(limit.children().get(0).children().size(), equalTo(1));
        assertThat(limit.children().get(0).children().get(0), instanceOf(EsqlUnresolvedRelation.class));
    }
    public void testLimitConstraints() {
        expectError("from text | limit -1", "extraneous input '-' expecting INTEGER_LITERAL");
    }
    public void testBasicSortCommand() {