```
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
for (Tuple<String, String> queryWithUnexpectedCmd : List.of(
            Tuple.tuple("from a | filter b > 1", "filter"),
            Tuple.tuple("from a | explain [ row 1 ]", "explain"),
            Tuple.tuple("from a | not-a-thing", "not-a-thing"),
            Tuple.tuple("from a | high5 a", "high5"),
            Tuple.tuple("from a | a+b = c", "a+b"),
            Tuple.tuple("from a | a//hi", "a"),
            Tuple.tuple("from a | a/*hi*/", "a"),
            Tuple.tuple("explain [ from a | evl b = c ]", "evl")
        )) {
            ParsingException pe = expectThrows(ParsingException.class, () -> statement(queryWithUnexpectedCmd.v1()));
            assertThat(
                pe.getMessage(),
                allOf(
                    containsString("mismatched input '" + queryWithUnexpectedCmd.v2() + "'"),
                    containsString("'eval'"),
                    containsString("'stats'"),
                    containsString("'where'")
                )
            );
        }
    }
    public void testDeprecatedIsNullFunction() {
        expectError(
            "from test | eval x = is_null(f)",
            "line 1:23: is_null function is not supported anymore, please use 'is null'/'is not null' predicates instead"
        );
        expectError(
            "row x = is_null(f)",
            "line 1:10: is_null function is not supported anymore, please use 'is null'/'is not null' predicates instead"