Basic Errors in the metadata?

[HExenweiss]

I have written a code in R where lat and long are read from two tables and plotted with different colors on a map.

Both tables are structured as follows:

(I checked all enterties and they are all correct)

But the enviroment look like this (this is maybe the reason for the error)

The code looks like this:

install.packages('readxl')
library(readxl)

data_a <- read_excel('C:/Users/Location_map.xlsx', sheet = 'Core_Tops')
data_b <- read_excel('C:/Users/Location_map.xlsx', sheet = 'Tows')
lat_a <- data_a$Lat
lon_a <- data_a$Long
lat_b <- data_b$Lat
lon_b <- data_b$Long

# until this point the code workes very well :D


install.packages('leaflet')
library(leaflet)

map <- leaflet() %>%
  addTiles() %>%
  addMarkers(lng = lon_a, lat = lat_a, icon = ~colorIcon("blue",iconSize = c(20, 20))) %>%
  addMarkers(lng = lon_b, lat = lat_b, icon = ~colorIcon("red",iconSize = c(20, 20)))

map

When I execute it I get the following error message:

Error in UseMethod("metaData"): inapplicable method for 'metaData' applied to object of class "NULL"

What could be the cause? I can not find any answeres!

[technocrat]

Before trying to figure out the meaning of the error message, convert the values of the character variables to numeric.

lat_a <- as.numeric(lat_a)
lon_a <- as.numeric(lon_a)

Data arriving from spreadsheets often show similar problems.