Reference.update failed: First argument contains a function in property code example

Example: [Unhandled promise rejection: Error: Reference.update failed: First argument contains undefined in property 'orders.-MN6f-JxMnLS4qAmVfs0.info.other_phone']

to make sure your object does not contain any undefined props use this simple trick:

JSON.parse( JSON.stringify(YourJsonData ) )
For more info take a look at this codePen: http://codepen.io/ajmueller/pen/gLaBLX