Change to Object.prototype.hasOwnProperty.call due to changes in node.js. Also check for null.

[mika-s]

I was getting this error message when using mongoose-patch-update with node.js v7.10:

TypeError: updateData.hasOwnProperty is not a function
at findOne.select.exec.then (C:\x\node_modules\mongoose-patch-update\index.js:34:43)
at newTickHandler (C:\x\node_modules\mpromise\lib\promise.js:234:18)
at _combinedTickCallback (internal/process/next_tick.js:73:7)
at process._tickCallback (internal/process/next_tick.js:104:9)

There have been some changes in node.js v.6.x that is the cause of this error. It's discussed here.

Another problem I had was when trying to update a field in the model that was null before. It gave the following error:

TypeError: Cannot convert undefined or null to object
at Function.keys ()
at findOne.select.exec.then (C:\x\node_modules\mongoose-patch-update\index.js:32:103)
at newTickHandler (C:\x\node_modules\mpromise\lib\promise.js:234:18)
at _combinedTickCallback (internal/process/next_tick.js:73:7)
at process._tickCallback (internal/process/next_tick.js:104:9),
status: 400 }

typeof modelInstance[attribute] == 'object' will return true when the type is null, so I added an extra check for null.

[jbutko]

Great thanks for the fix.