FIXed test on existence of javastics path in model_options in case pa…

…ram_values is specified.

The test was crashing in case javastics==NULL, (which is possible if not given to stics_wrapper_options when initializing model_options, for example).
The case javastics=="unknown" is not possible at this step since it is already captured above in do.call(stics_wrapper_options, model_options).

R/stics_wrapper.R

@@ -152,9 +152,10 @@ stics_wrapper <- function(model_options,
   javastics <- model_options$javastics
 
   # Checking if javastics path is set when forcing parameters
-  if (!is.null(param_values) && javastics == "unknown")
+  if (!is.null(param_values) && is.null(javastics))
     stop(paste0("When parameters values are to be forced,",
-                " a JavaStics path must be set in model_options list !"))
+                " a JavaStics path must be set in model_options list",
+                " (see javastics argument of stics_wrapper_options function)."))
 
   # In case of successive USMs, disable parallel run
   if (!is.null(successive_usms)) parallel <- FALSE