fix(flux.uncertainty): prevent crash when positive-flux model is not fitted

modules/uncertainty/NEWS.md

@@ -1,5 +1,10 @@
 # PEcAn.uncertainty 1.9.0.9000
 
+## Fixed
+
+* `flux.uncertainty()`: removed a duplicate assignment of `E2` (the same line appeared twice in sequence with no effect except wasted computation).
+* `flux.uncertainty()`: fixed a crash that occurred when all positive-flux magnitude bins contained `NA` error estimates. In that case the positive-slope model `mp` was never assigned, but the `else` branch for the negative-slope fallback unconditionally referenced `mp$coefficients[1]`, producing an "object 'mp' not found" error. The fallback now uses `else if (exists("mp", inherits = FALSE))` so it only runs when `mp` was actually fitted.
+
 * Multiple bugfixes in `input.ens.gen()` handling of parent ids (#3783):
     - No longer skips inputs that have a parent but no sampling method.
     - Argument `parent_ids` now accepts integer vectors even if not wrapped in a list.

modules/uncertainty/R/flux_uncertainty.R

@@ -105,23 +105,22 @@ flux.uncertainty <- function(measurement, QC = 0, flags = TRUE, bin.num = 10,
   ## would be better to fit a two line model with a common intercept, but this
   ## is quicker to implement for the time being
   E2 <- errBin - errBin[zero]
-  E2 <- errBin - errBin[zero]
   intercept <- errBin[zero]
-  
-  return.list <- list(mag = magBin, 
-                      err = errBin, 
-                      bias = biasBin, 
+
+  return.list <- list(mag = magBin,
+                      err = errBin,
+                      bias = biasBin,
                       n = nBin,
                       intercept = intercept)
-  
-  if(!all(is.na(E2[pos]))){
+
+  if (!all(is.na(E2[pos]))) {
     mp <- stats::lm(E2[pos] ~ magBin[pos] - 1)
     return.list$slopeP <- mp$coefficients[1]
-  } 
-  if(!all(is.na(E2[neg]))){
+  }
+  if (!all(is.na(E2[neg]))) {
     mn <- stats::lm(E2[neg] ~ magBin[neg] - 1)
     return.list$slopeN <- mn$coefficients[1]
-  }else{
+  } else if (exists("mp", inherits = FALSE)) {
     return.list$slopeN <- mp$coefficients[1]
   }