1. Bugfix for hardcoded xlab

2. Use na.rm when determining axis limits for night shading to be
   compatible with plotting with some missing values

R/plot.vpi.R

@@ -116,7 +116,7 @@ plot.vpi <- function(x, quantity = "mtr", xlab = "time",
 
   # plot the data
   plot(x$datetime, x[quantity][[1]],
-    type = "l", xlab = "time", ylab = ylab,
+    type = "l", xlab = xlab, ylab = ylab,
     ylim = ylim, main = main, xaxs = "i", yaxs = "i", ...
   )
 
@@ -145,8 +145,8 @@ plot.vpi <- function(x, quantity = "mtr", xlab = "time",
     # determine the plot range of the night time shading
     if (missing(ylim)) {
       pol.range <- c(
-        min(c(0, 2 * min(x[quantity][[1]]))),
-        2 * max(x[quantity][[1]])
+        min(c(0, 2 * min(x[quantity][[1]], na.rm = TRUE))),
+        2 * max(x[quantity][[1]], na.rm = TRUE)
       )
     } else {
       pol.range <- ylim
@@ -167,7 +167,7 @@ plot.vpi <- function(x, quantity = "mtr", xlab = "time",
     # plot the data again on top of the shading
     graphics::points(x$datetime, x[quantity][[1]],
       type = "l",
-      xlab = "time", ylab = ylab, ylim = ylim, main = main, ...
+      xlab = xlab, ylab = ylab, ylim = ylim, main = main, ...
     )
   }
 }