Method is_unknown

datafusion/expr/src/expr.rs:1976–1978

Return `IsUnknown(Box(self))`

(self)

    /// Return `IsUnknown(Box(self))`
    pub fn is_unknown(self) -> Expr {
        Expr::IsUnknown(Box::new(self))
    }

    /// Return `IsNotUnknown(Box(self))`
    pub fn is_not_unknown(self) -> Expr {