Fix: random bug on Travis

test/integration/tools/node.js

@@ -100,11 +100,13 @@ function Node (dbName, options) {
         BlockchainService.prove(block, sigFunc, difficulty, next);
       },
       function (provenBlock, next){
+        if (provenBlock) {
           logger.debug(provenBlock.getRawSigned());
           post('/blockchain/block', {
             "block": provenBlock.getRawSigned()
           }, next);
         }
+      }
     ], done);
   }