Keep all variables after every iteration - r

Question

Using the following snippet it is possible to iterate two api call in json format
At the end of the loop there is a command with transforms json to data frame
How is it possible to keep in every iteration all these variables and fill NA if a value in the specific variable does not exist in a specific iteration?
library(jsonlite)
library(httpuv)
library(httr)
myapp <- oauth_app(appname = "insert_your_credentials",
key = "insert_your_credentials",
secret = "insert_your_credentials")
github_token <- oauth2.0_token(oauth_endpoints("github"), myapp)
gtoken <- config(token = github_token)
df <- data.frame(link = c("https://api.github.com/search/commits?q=%22image%22+AND+%22covid%22?page=1&per_page=100", "https://api.github.com/search/commits?q=%22image%22+AND+%22covid%22?page=2&per_page=100"))
for (i in 1:nrow(df)) {
req <- GET(df$link[i])
# Extract content from a request
json1 = content(req)
# Convert to a data.frame
char <- rawToChar(req$content)
dfcollection <- jsonlite::fromJSON(char)
}

Answer 1

It may be wrapped with tryCatch or possibly from purrr. Below code uses possibly
library(purrr)
library(jsonlite)
convertToJSON <- function(x)
{
req <- GET(x)
# Extract content from a request
json1 = content(req)
# Convert to a data.frame
char <- rawToChar(req$content)
dfcollection <- jsonlite::fromJSON(char)
return(dfcollection)
}
pconvertToJSON <- possibly(convertToJSON, otherwise = NA)
out <- map(df$link, pconvertToJSON)