risingwavelabs/risingwave · error · ExprError

field name must not be null

Error message

field name must not be null

What it means

ExprError::FieldNameNull is thrown when a field name used to access or construct a struct/object field is NULL. Field access by name requires a non-null name string; a null name is meaningless and rejected rather than producing a null result.

Solutions

1. Coalesce the field name to a safe default: `get_field(obj, COALESCE(name_col, 'default_field'))`.
2. Filter rows with NULL names before the field access.
3. Fix upstream data so field-name columns are NOT NULL.

Example fix

// before
SELECT get_field(payload, name_col) FROM t;
// after
SELECT CASE WHEN name_col IS NOT NULL THEN get_field(payload, name_col) ELSE NULL END FROM t;

-- guard null field names before get_field
SELECT CASE WHEN name_col IS NOT NULL THEN get_field(obj, name_col) ELSE NULL END FROM t;

// Null field name is bad input: return NULL row result instead of failing
if err.to_string().contains("field name must not be null") {
    return Ok(None);
}

When it happens

Trigger: Evaluating a `get_field`-style expression where the field-name argument is NULL (e.g. `get_field(obj, some_nullable_col)` where the column is NULL), or constructing structs with a null field name.

Common situations: Nullable name columns from upstream data used as field keys, joins that null out the key column, ETL pipelines where field names are computed dynamically.

Related errors

• Invalid struct encoding
• null value in column
• variant object cannot have duplicate field name
• {0}
• {0}

AI-assisted analysis of risingwavelabs/risingwave@6469eb736d (2026-09-11). Data as JSON: /api/errors/f3202550b2f25d99. Report an issue: GitHub.

Appendix: source

Thrown at src/expr/core/src/error.rs:105

    #[error("More than one row returned by {0} used as an expression")]
    MaxOneRow(&'static str),

    /// TODO: deprecate in favor of `Function`
    #[error(transparent)]
    Internal(
        #[from]
        #[backtrace]
        anyhow::Error,
    ),

    #[error("not a constant")]
    NotConstant,

    #[error("Context {0} not found")]
    Context(&'static str),

    #[error("field name must not be null")]
    FieldNameNull,

    #[error("too few arguments for format()")]
    TooFewArguments,

    #[error(
        "null value in column \"{col_name}\" of relation \"{table_name}\" violates not-null constraint"
    )]
    NotNullViolation {
        col_name: Box<str>,
        table_name: Box<str>,
    },

    #[error("invalid state: {0}")]
    InvalidState(String),

    /// Function error message returned by UDF.
    /// TODO: replace with `Function`

View on GitHub (pinned to 6469eb736d)