Small change to PoissonNode to deal with cases when the length of the mean...

Small change to PoissonNode to deal with cases when the length of the mean value is different to the offset.  Usual R conventions apply here.

R/node.R

@@ -208,7 +208,8 @@ PoissonNode <- R6::R6Class(
         self$addParent(offset, 'offset')
     },
     logDensity = function() {
-      lambda <- sapply(self$parents, function(parent) parent$getData())
+      lambda <- as.data.frame(sapply(self$parents,
+                                     function(parent) parent$getData()))
       lambda <- apply(lambda, 1, prod)
       sum(dpois(self$data, lambda, log = T))
     }