diff --git a/mysql-test/main/opt_trace.result b/mysql-test/main/opt_trace.result
index 82cb7478405..12d4c713886 100644
--- a/mysql-test/main/opt_trace.result
+++ b/mysql-test/main/opt_trace.result
@@ -6021,4 +6021,17 @@ t_outer_2.a in (select t_inner_3.a from t2 t_inner_3, t1 t_inner_4)	{
 }	0	0
 set @@optimizer_switch= @save_optimizer_switch;
 drop table t1,t2;
+#
+# MDEV-18942: Json_writer::add_bool: Conditional jump or move depends on uninitialised value upon 
+# fulltext search under optimizer trace
+#
+CREATE TABLE t1 (f VARCHAR(255), FULLTEXT(f));
+CREATE VIEW v1 AS SELECT * FROM t1;
+INSERT INTO t1 VALUES ('fooba'),('abcde'),('xyzab');
+SET optimizer_trace = 'enabled=on';
+SELECT COUNT(*) FROM v1 WHERE MATCH (f) AGAINST ('fooba');
+COUNT(*)
+1
+DROP VIEW v1;
+DROP TABLE t1;
 set optimizer_trace='enabled=off';
diff --git a/mysql-test/main/opt_trace.test b/mysql-test/main/opt_trace.test
index e59a11fbfc3..4ec7c338acd 100644
--- a/mysql-test/main/opt_trace.test
+++ b/mysql-test/main/opt_trace.test
@@ -373,4 +373,18 @@ explain select * from t1 t_outer_1,t2 t_outer_2  where t_outer_1.a in (select t_
 select * from INFORMATION_SCHEMA.OPTIMIZER_TRACE;
 set @@optimizer_switch= @save_optimizer_switch;
 drop table t1,t2;
+
+--echo #
+--echo # MDEV-18942: Json_writer::add_bool: Conditional jump or move depends on uninitialised value upon 
+--echo # fulltext search under optimizer trace
+--echo #
+
+CREATE TABLE t1 (f VARCHAR(255), FULLTEXT(f));
+CREATE VIEW v1 AS SELECT * FROM t1;
+INSERT INTO t1 VALUES ('fooba'),('abcde'),('xyzab');
+SET optimizer_trace = 'enabled=on';
+SELECT COUNT(*) FROM v1 WHERE MATCH (f) AGAINST ('fooba');
+DROP VIEW v1;
+DROP TABLE t1;
+
 set optimizer_trace='enabled=off';
diff --git a/sql/sql_select.cc b/sql/sql_select.cc
index 644746d14bb..c619cd4e066 100644
--- a/sql/sql_select.cc
+++ b/sql/sql_select.cc
@@ -6487,6 +6487,7 @@ add_ft_keys(DYNAMIC_ARRAY *keyuse_array,
   keyuse.keypart_map= 0;
   keyuse.sj_pred_no= UINT_MAX;
   keyuse.validity_ref= 0;
+  keyuse.null_rejecting= FALSE;
   return insert_dynamic(keyuse_array,(uchar*) &keyuse);
 }