It's relatively easy to incorrectly use the WT_CONFIG_ITEM fields, for example, this code from WT-4939:

WT_RET(__wt_config_gets(session, cfg, "name", &cval));
if (cval.val != 0)
        return (0);

which is retrieving a value for a string configuration, but testing an integer configuration and so always returns. The correct test would have been:

WT_RET(__wt_config_gets(session, cfg, "name", &cval));
if (cval.len != 0)
        return (0);

It might be reasonable to add WT_CONFIG_ITEM accessor functions that use the WT_CONFIG_ITEM.type field to avoid making the wrong test.