error: 4 arguments passed to 'for' which requires 3

This is my code and the for loop is giving me the error: 4 arguments passed to for which requires 3. and I tried to move the loop to include all the leaflet but still same error.

library(shiny)
library(rgdal)
library(DT)
library(dygraphs)
library(xts)
library(leaflet)
library(igraph)
library(RMySQL)
library(DBI)
library(magrittr)

#creat connection to database
con <- dbConnect(RMySQL::MySQL(), user = "root", pass = "",
             servername = "localhost", db = "brest")

#dbListTables(con)
#dbListFields(con, "nodes")


r_colors <- rgb(t(col2rgb(colors()) / 255))
names(r_colors) <- colors()


ui <- fluidPage(

titlePanel(p("Maritime Map", style = "color:#3474A7")),

tabPanel("Reactive Map", 

       #SideBarLayout for sidebar Panel for the options of the map       
       sidebarLayout(

         #SideBar Panel with options to adjust the map
         sidebarPanel(  

         ),

         #Main panel to put plots  
         mainPanel(leafletOutput("map", height = 600))
       )
  )



 )

server <- function(input, output, session) {

  #select all nodes table
  rs = dbSendQuery(con, "SELECT * FROM nodes")
 datas = fetch(rs, n=6)
  dbClearResult(dbListResults(con)[[1]])

  #select all edges table
  ed = dbSendQuery(con, "SELECT * FROM edge")
  edg = fetch(ed, n=-1)
  dbClearResult(dbListResults(con)[[1]])

  #select edge_id from table edge
  edid = dbSendQuery(con, "SELECT edge_id FROM edge")
  edgid = fetch(edid, n=-1)
  dbClearResult(dbListResults(con)[[1]])

  #get  number of rows in table edge
  numr = dbSendQuery(con, "SELECT COUNT(*) FROM edge")
  numm = fetch(numr, n=-1)
  nmb <- as.numeric(numm)

  pall <- colorFactor(c("navy", "red", "green", "yellow"), 
                  domain = c("port", "anchorage", "turningpoint", "marina"))

  output$map <- renderLeaflet({



    leaflet() %>%

  addProviderTiles(providers$Esri.OceanBasemap, 
                   options = providerTileOptions(noWrap = TRUE)) %>%

  addCircleMarkers(data = datas, weight = 3, radius= 10, color = ~pall(node_type),  group = "detail",
                   stroke = F, fillOpacity = 0.5, clusterOptions = markerClusterOptions()) %>%

This is the for loop. when including all the leaflet in the loop I get the

error: invalid (NULL) left side of assignment.

    for (i in 1:nmb) {

    #select source node
    src = dbSendQuery(con, "SELECT source_node_id FROM edge WHERE edge_id = 'i'")
    srcc = fetch(src, n=-1)
    srid <- as.numeric(srcc)
    dbClearResult(dbListResults(con)[[1]])

    #select longitude and latitude of source node
    slonlat1 = dbSendQuery(con, "SELECT lon, lat FROM nodes WHERE node_id = 'srid'")
    slonlat2 = fetch(slonlat1, n=-1)
    dbClearResult(dbListResults(con)[[1]])

    #select target node
    tar = dbSendQuery(con, "SELECT target_node_id FROM edge WHERE edge_id = 'i'")
    tarr = fetch(tar, n=-1)
    trid <- as.numeric(tarr)
    dbClearResult(dbListResults(con)[[1]])

    #select longitude and latitude of target node
    tlonlat1 = dbSendQuery(con, "SELECT lon, lat FROM nodes WHERE node_id = 'trid'")
    tlonlat2 = fetch(tlonlat1, n=-1)
    dbClearResult(dbListResults(con)[[1]])

    dd <- data.frame(x=slonlat2, y=tlonlat2)

   # addPolylines(data = dd, lng = ~lon, lat = ~lat)
  }

  groupOptions("details", zoomLevels = 10:30) %>%

  addLegend("bottomright", colors= c("green", "navy", "yellow", "red"), 
            labels=c("port", "anchorage", "turningpoint", "marina"), title="Maritime")

  })

}

shinyApp(ui, server)

thanks for your help