Skip checking parameters of nonparametric distributions (#750)

* Skip checking parameters of nonparametric distributions

* Fix distribution getting step of composite distribution

* Add NEWS item

* Fix code style

NEWS.md

@@ -21,6 +21,7 @@
 - a bug was fixed where `forecast_secondary()` did not work with fixed delays. By @sbfnk in #717 and reviewed by @seabbs.
 - a bug was fixed that caused delay option functions to report an error if only the tolerance was specified. By @sbfnk.
 - a bug was fixed that led to the truncation PMF being shortened from the wrong side when the truncation PMF was longer than the supplied data. By @seabbs in #736 and reviewed by @sbfnk and @jamesmbaazam.
+- a bug was fixed that caused internal validation checks on delay distributions to fail if they contained non-parametric distributions. By @jamesmbaazam in #750 and reviewed by @seabbs.
 
 ## Documentation
 

R/checks.R

@@ -81,12 +81,14 @@ check_stan_delay <- function(dist) {
   # Check that `dist` has parameters that are either numeric or normal
   # distributions with numeric parameters and infinite maximum
   numeric_or_normal <- unlist(lapply(seq_len(ndist(dist)), function(id) {
-    params <- get_parameters(dist, id)
-    vapply(params, function(x) {
-      is.numeric(x) ||
-        (is(x, "dist_spec") && get_distribution(x) == "normal" &&
-           is.infinite(max(x)))
-    }, logical(1))
+    if (get_distribution(dist, id) != "nonparametric") {
+      params <- get_parameters(dist, id)
+      vapply(params, function(x) {
+        is.numeric(x) ||
+          (is(x, "dist_spec") && get_distribution(x) == "normal" &&
+             is.infinite(max(x)))
+      }, logical(1))
+    }
   }))
   if (!all(numeric_or_normal)) {
     stop(