PVS-Studio warning V527 for Apache

typedef struct {
    const char* (*func)(request_rec *r,char *arg);
    char *arg;
} format_tag;

static char *parse_format_tag(apr_pool_t *p,
                              format_tag *tag,
                              const char **sa)
{
  ...
  tag->arg = '\0';
  ...
}

This is what should have been written here: tag->arg = NULL; or tag->arg[0] = '\0';.

This suspicious code was found in Apache project by PVS-Studio static code analyzer.
Warning message is:
V527 It is odd that the '\0' value is assigned to 'char' type pointer. Probably meant: *tag->arg = '\0'. mod_headers mod_headers.c 330

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