Function get_null_physical_expr_pair 

fn get_null_physical_expr_pair(
    expr: &Expr,
    input_dfschema: &DFSchema,
    input_schema: &Schema,
    session_state: &SessionState,
) -> Result<(Arc<dyn PhysicalExpr>, String)>

For a given logical expr, get a properly typed NULL ScalarValue physical expression