test before adding/removing

remix-lib/src/execution/execution-context.js

@@ -136,14 +136,18 @@ function ExecutionContext () {
   }
 
   this.removeProvider = function (name) {
+    if (name && this.customNetWorks[name]) {
       delete this.customNetWorks[name]
       self.event.trigger('removeProvider', [name])
     }
+  }
 
   this.addProvider = function (network) {
+    if (network && network.name && network.url) {
       this.customNetWorks[network.name] = network
       self.event.trigger('addProvider', [network])
     }
+  }
 
   this.internalWeb3 = function () {
     return web3