testlist <- list(data = c("vwqsmdzzqwjrhymjmncf", NA, "ufahkyfhjgskpohfyxzm",  "sjlngnwvrzhgepktmzot", "vgyvqbrusvjgdnxgeqas", "nobzcmwoshbhfhraomz",  "mdwvawhtyvnyozkpr", "mmwwwbqsmtbsxrbyuvwb", "bmllvzynloxwun",  "yevuvcziik", "otxevodhvnvcbnzclolk", "oagnygbnrjbbnil", "rmliiqolkn",  "ptrukg", "iltpuydecwmfxe", NA, NA, NA, "cfgbinwlowvbdhmavrfb",  "ihozmlwcgtykvmufnq", "lesglplolsylxcudbnxj", "udezecjhfardymjrxamb",  NA, NA, NA, NA, "kprzsquis", NA, NA, "gqvqnqpzbbfqtuyqmogm",  "fivhtxolyrlkkxnvdtis", "rghfzpuighihynftlgwz", NA, "cfcsweneyqpxhchczuwi",  NA, "huwpzogyfnlmowx", NA, "tquum", "zmjyrbwftkly", "pzulgvvacker",  "yjlfzcrskcxqwyxubmkb", "kzkxokqgqwcmdszxezic", "mtdngwpsqmuggpk",  NA, "fnztqkqsvqztvloqhryy", NA, NA, NA, "klmhewqnjpqidw", "bkrffxuwgxosoxiqkidf",  "zkx", "tggmlfvpyqhwhibzdcdj"), ease = c("mydsqtwarzlhpxfviisa",  NA, NA, "mesdwlxmuh", "wmznqi", "eahpfklwolj", "uarkoclrmicfpgxtezpy",  "ppxuvudsrymwhjwffjwo", "t", "hrbaveestfbojm", "xqkmutrekdfk",  NA, "temmkdqhitfnonlgzxkk", "qmeounsjgftuufapllhg", "jvpskltbbqmioonldayq",  "szkxjpzuzqkfxlvaylwe", "paepccduspcagvumxvao", NA, NA, NA, NA,  "tscuvamsvr", NA, NA, "nhlyzivlrihvhpmanshh", "wywadecamsmxffgltogx",  NA, "fhjhpsmoeoarzmiyjpke", "aayaupqmjlfwkziedqbs", "gsoeqjikwncrngdxjque",  NA, "nknopxxjobzzmzxnajyz", "gvvummylzxeyib", NA, "ttecsoaliikosukyfkr",  "relizwyyqcymknvakvcv"))
result <- do.call(tweenr:::constant_fill_interpolator,testlist)
str(result)