Optimizer Trace shows "unprintable_geometry_value" for GIS ranges

CREATE TABLE t1 (

  g GEOMETRY NOT NULL,

  SPATIAL KEY (g)

);

insert into t1 

select ST_GeomFromText(CONCAT('POINT(', seq,' ', seq ,')')) from seq_1_to_1000;

set optimizer_trace=1;

explain

select * from t1 

where ST_Overlaps(g, ST_GeomFromText('POLYGON((0 0, 0 10, 10 10, 10 0, 0 0))'));

select * from information_schema.optimizer_trace;

                    "range_scan_alternatives": [

                      {

                        "index": "g",

                        "ranges": ["(g) (unprintable_geometry_value)"],

                        "rowid_ordered": false,

                        "using_mrr": false,

                        "index_only": false,

                        "rows": 1,

                        "cost": 0.00424968,

                        "chosen": true

                      }

      "multi_range_read_info_const_calls": [

        {

          "index_name": "g",

          "ranges": ["(g) (unprintable_geometry_value)"],

          "num_rows": 53,

          "cost": {

            "avg_io_cost": 0.0002048,

            "cpu_cost": 0,

            "comp_cost": 0.001696,

            "copy_cost": 0,

            "limit_cost": 0,

            "setup_cost": 0.00079112,

            "index_cost_io": 4,

            "index_cost_cpu": 0.00607372,

            "row_cost_io": 20,

            "row_cost_cpu": 0.04570932

          },

ST_Envelope(ST_GeomFromText('LINESTRING(0 0, 10 5)'))