Don't emit errors when there are no listeners for the error event as …

…it results in unhandled errors

package.json

@@ -1,6 +1,6 @@
 {
   "name": "@iflix/json-rules-engine",
-  "version": "4.0.0",
+  "version": "4.0.1",
   "description": "Rules Engine expressed in simple json",
   "main": "dist/index.js",
   "scripts": {

src/engine.js

@@ -198,7 +198,7 @@ class Engine extends EventEmitter {
           this.emit('failure', rule.event, almanac, ruleResult)
         }
       }).catch((error) => {
-        this.emit('error', error)
+        this.listenerCount('error') > 0 && this.emit('error', error)
         throw error
       })
     }))
@@ -224,7 +224,7 @@ class Engine extends EventEmitter {
       debug(`engine::run ruleResult:${ruleResult.result}`)
       return ruleResult
     }).catch((error) => {
-      this.emit('error', error)
+      this.listenerCount('error') > 0 && this.emit('error', error)
       throw error
     })
   }

src/rule.js

@@ -275,7 +275,7 @@ class Rule extends EventEmitter {
       error.rule = {
         name: this.name
       }
-      this.emit('error', error)
+      this.listenerCount('error') > 0 && this.emit('error', error)
       throw error
     }