r - Empty textInput() causing error in leaflet shiny app - r

Question

I have a shiny app that plots data from an API on a leaflet map. It also takes 2 inputs from the user that are passed through to the API call.
One of those is a text input that sets the region for which the API should pull data. If the user types in an incorrect region code or simply deletes the code, the shiny app gives an error and then you have to type in a correct code and wait for the app to get back on track. It's clumsy and looks bad.
I tried to get around it by using if(is.null(APIdata())) with an if{}else{} (see code below), but this literally did not change anything. I thought it would work, and I'm fine with the idea of it just popping back to an empty leaflet. Is there something else I can do?
Error:
Error: parse error: premature EOF
(right here) ------^
and
Warning: Error in : parse error: premature EOF
(right here) ------^
Stack trace (innermost first):
96: parse_string
95: parseJSON
94: fromJSON_string
93: jsonlite::fromJSON
92: ebird_GET
91: ebirdnotable
90: <reactive:APIdata> [/Users/Guest/Desktop/eBirdRarity/app.R#41]
79: APIdata
78: func [/Users/Guest/Desktop/eBirdRarity/app.R#68]
77: origRenderFunc
76: output$myMap
1: runApp
Code:
library(shiny)
library(shinydashboard)
library(shinythemes)
library(leaflet)
library(leaflet.extras)
library(rebird)
ui <- bootstrapPage(
theme = shinytheme("superhero"),
# Setting map to full-screen
tags$style(type="text/css", "html, body {width:100%;height:100%}"),
# Initializing leaflet output
leafletOutput("myMap", width="100%", height="100%"),
# Adding title overlayed on leaflet map
absolutePanel(top = 1, left = 50, draggable = T,
titlePanel("eBird Recent Rarities Viewer")),
# Adding slider input overlayed on leaflet map
absolutePanel(bottom = 1, left = 45, draggable = T,
sliderInput("slider_in", "Days Back", min = 1, max = 30, value = 14, round = T)),
# Adding text input overlayed on leaflet map
absolutePanel(top = 1, right = 45, draggable = T,
textInput("region_in", "Region Code", value = "US-MA", placeholder = "US-MA"))
)
server <- function(input, output) {
# Rendering data frame from API with slider input
APIdata <- reactive({
# Initial fetch of data from eBird API
a <- ebirdnotable(region = as.character(input$region_in), back = as.numeric(input$slider_in))
# Changing review status from logical to numeric
cols <- sapply(a, is.logical)
a[,cols] <- lapply(a[,cols], as.numeric)
# Initializing new date column
a["date"] <- format(strptime(a$obsDt, format = "%Y-%m-%d"), "%b %d")
# Initializing new color grouping column
a["group"] <- NA
# Assigning colors by review status
idx<- (a$obsReviewed == 0) # Not reviewed
a$group[idx] <- "white"
idx<- (a$obsReviewed == 1) & (a$obsValid == 1) # Reviewed and accepted
a$group[idx] <- "green"
# Jittering lat/lon points to fix point overlap
a$lat = jitter(a$lat, factor = 3)
# print(a)
return(a)
})
# Leaflet map
output$myMap = renderLeaflet({
if(is.null(APIdata()))
{
# Rendering leaflet map
return(leaflet() %>% addTiles()) %>%
addSearchOSM(options = searchOSMOptions(zoom = 8))
}
else
{
# Splitting up by review status in order to show reviewed on top
notReviewed = APIdata()[APIdata()$group == "white",]
accepted = APIdata()[APIdata()$group == "green",]
# Rendering leaflet map
leaflet() %>% addTiles() %>%
addCircleMarkers(data = notReviewed, color = "white", opacity = 0.7, label = paste(notReviewed$comName,", ",notReviewed$date, ", ", notReviewed$locName,sep = "")) %>% # , labelOptions = labelOptions(noHide = F, direction = 'auto')) %>%
addCircleMarkers(data = accepted, color = "green", opacity = 0.7, label = paste(accepted$comName,", ",accepted$date, ", ", accepted$locName, sep = "")) %>% # , labelOptions = labelOptions(noHide = F, direction = 'auto')) %>%
addLegend(position = "bottomright",
colors = c("#FFFFFF", "#008000"),
labels = c("Not reviewed", "Accepted"),
title = "Legend: review status", opacity = 1) %>%
addSearchOSM(options = searchOSMOptions(zoom = 8))
}
})
}
# Run the application
shinyApp(ui = ui, server = server)

Answer 1

You could just validate if you are getting a tibble with values or if you are getting an empty tibble. In case the tibble is empty you can return NULL. This way the validation you have added to check if APIdata() is NULL would work.
You could just add if(length(a) == 0){return(NULL)} after a <- ebirdnotable(region = as.character(input$region_in), back = as.numeric(input$slider_in)) in your reactive for it to work.
EDIT:
As you mentioned in your comment you can actually use try here. That would mean adding one more condition in addition to above condition the code would be something like this:
a <- try(ebirdnotable(region = as.character(input$region_in), back = as.numeric(input$slider_in)))
if(class(a) == "try-error" ||length(a) == 0){return(NULL)}
Hope it helps!