After upgrading from node v0.12.7 to v4.2.3 our application crashes every few hours or after 1 or 2 days with the following uncaught exception: ``` TypeError: Cannot read property 'callback' of undefined at process._tickCallback (node.js:341:26) ``` Could this be a bug in node.js? The code in src/node.js doesn't look like `tock` is expected to be undefined: ``` javascript // Run callbacks that have no domain. // Using domains will cause this to be overridden. function _tickCallback() { var callback, args, tock; do { while (tickInfo[kIndex] < tickInfo[kLength]) { tock = nextTickQueue[tickInfo[kIndex]++]; callback = tock.callback; // <------- line 341. tock is undefined args = tock.args; ```