Improve error handling: if a requested pattern partial is missing, say

so; if there's compilation error, print the output from the exception.

Author: geoffp

lib/engine_underscore.js

@@ -32,7 +32,10 @@ function addParentContext(data, currentContext) {
 
 _.mixin({
   renderNamedPartial: function (partialKey, data, currentContext) {
-    return _.renderPartial(partialRegistry[partialKey], data, currentContext);
+    var partialString = partialRegistry[partialKey];
+    if (typeof partialString !== 'string') { throw `Pattern ${partialKey} not found.`; }
+
+    return _.renderPartial(partialString, data, currentContext);
   },
   renderPartial: function (partial, dataIn, currentContext) {
     var data = dataIn || {};
@@ -81,7 +84,7 @@ var engine_underscore = {
     try {
       compiled = _.template(pattern.extendedTemplate);
     } catch (e) {
-      console.log(`Error compiling template ${pattern.patternName}:`, pattern.extendedTemplate);
+      console.log(`Error compiling underscore template ${pattern.patternName}:`, pattern.extendedTemplate, e);
     }
 
     // This try-catch is necessary because references to undefined variables