Sending several values from server

To pass multiple elements to update:

1. We can use shiny:::dropNulls internal function to ensure that the list does not contain NULL elements.
2. Pass the list to the sendInputMessage.

updateCustomTextInput <- function(
  inputId, 
  value = NULL, 
  placeholder = NULL, 
  session = getDefaultReactiveDomain()
) {
  message <- dropNulls(
    list(
      value = value,
      placeholder = placeholder
    )
  )
  session$sendInputMessage(inputId, message)
}