```
from employees | keep * | mv_expand first_name
```

throws UnresolvedException:

```
org.elasticsearch.xpack.ql.capabilities.UnresolvedException: Invalid call to attribute on an unresolved object ?*
        at org.elasticsearch.xpack.ql.expression.UnresolvedNamedExpression.toAttribute(UnresolvedNamedExpression.java:44)
        at org.elasticsearch.xpack.ql.expression.Expressions.asAttributes(Expressions.java:40)
        at org.elasticsearch.xpack.ql.plan.logical.Project.output(Project.java:62)
        at org.elasticsearch.xpack.esql.plan.logical.MvExpand.<init>(MvExpand.java:31)
        at org.elasticsearch.xpack.esql.parser.LogicalPlanBuilder.lambda$visitMvExpandCommand$3(LogicalPlanBuilder.java:154)
        at org.elasticsearch.xpack.esql.parser.LogicalPlanBuilder.visitCompositeQuery(LogicalPlanBuilder.java:89)
        at org.elasticsearch.xpack.esql.parser.LogicalPlanBuilder.visitCompositeQuery(LogicalPlanBuilder.java:66)
        at org.elasticsearch.xpack.esql.parser.EsqlBaseParser$CompositeQueryContext.accept(EsqlBaseParser.java:232)
        at org.elasticsearch.xpack.ql.parser.ParserUtils.typedParsing(ParserUtils.java:51)
        at org.elasticsearch.xpack.esql.parser.LogicalPlanBuilder.plan(LogicalPlanBuilder.java:73)
        at org.elasticsearch.xpack.esql.parser.LogicalPlanBuilder.visitSingleStatement(LogicalPlanBuilder.java:82)
        at org.elasticsearch.xpack.esql.parser.LogicalPlanBuilder.visitSingleStatement(LogicalPlanBuilder.java:66)
        at org.elasticsearch.xpack.esql.parser.EsqlBaseParser$SingleStatementContext.accept(EsqlBaseParser.java:169)
```

The problem is that MV_EXPAND tries to pre-calculate the output too early, when the resolution did not happen yet.
x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/parser/StatementParserTests.java
)
            );
        }
    }
    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"
        );
    }
    public void testMetadataFieldOnOtherSources() {
        expectError(
            "row a = 1 [metadata _index]",
            "1:11: mismatched input '[' expecting {<EOF>, '|', 'and', ',', 'or', '+', '-', '*', '/', '%'}"
        );
        expectError("show functions [metadata _index]", "line 1:16: token recognition error at: '['");
        expectError("explain [from foo] [metadata _index]", "line 1:20: mismatched input '[' expecting {'|', ',', OPENING_BRACKET, ']'}");
    }
    public void testMetadataFieldMultipleDeclarations() {
        expectError("from test [metadata _index, _version, _index]", "1:40: metadata field [_index] already declared [@1:21]");
    }
    public void testMetadataFieldUnsupportedPrimitiveType() {
        expectError("from test [metadata _tier]", "line 1:22: unsupported metadata field [_tier]");
    }
    public void testMetadataFieldUnsupportedCustomType() {
        expectError("from test [metadata _feature]", "line 1:22: unsupported metadata field [_feature]");