MDEV-5520 Connection lost on wrong CREATE ROLE

mysql-test/suite/roles/create_and_drop_role.result

@@ -34,3 +34,5 @@ ERROR HY000: Operation DROP ROLE failed for 'dummy'
 drop user dummy@'';
 select user, host, is_role from user where user like 'test%';
 user	host	is_role
+create role '';
+ERROR OP000: Invalid role specification ``.

mysql-test/suite/roles/create_and_drop_role.test

@@ -18,7 +18,6 @@ select user, host, is_role from user where user like 'test%';
 drop role test_role1;
 drop role test_role2, test_role3;
 
-
 create role test_role1;
 --error ER_CANNOT_USER
 create role test_role1;
@@ -45,3 +44,11 @@ drop user dummy@'';
 --sorted_result
 select user, host, is_role from user where user like 'test%';
 disconnect mysql;
+connection default;
+
+#
+# MDEV-5520 Connection lost on wrong CREATE ROLE
+#
+--error ER_INVALID_ROLE
+create role '';
+

sql/sql_acl.cc

@@ -800,7 +800,7 @@ ACL_ROLE::ACL_ROLE(const char * rolename, ulong privileges, MEM_ROOT *root) :
 
 static bool is_invalid_role_name(const char *str)
 {
-  if (strcasecmp(str, "PUBLIC") && strcasecmp(str, "NONE"))
+  if (*str && strcasecmp(str, "PUBLIC") && strcasecmp(str, "NONE"))
     return false;
 
   my_error(ER_INVALID_ROLE, MYF(0), str);