I just ran into the same issue. Was this already filed/solved in a later Mendix release?
We encountered a similar issue: after clicking Cancel, an error message appears: "An error occured, please contact your system administrator." The logging shows: "Cannot read property 'attributes' of null TypeError: Cannot read property 'attributes' of null"
It turned out that this problem arises on a page with:
* A text widget with a parameter that refers to another object, AND
* A data view (over association) that refers to the same other object.
Seen in Mendix 7.13.1 and 7.15.1.
I have filed a ticket for this: #65769
We have a workaround: enclose the text widget by a Data view that loads the referred object.
Maybe there is a resemblance with your situation.
For people reading in the future, this issue was indeed fixed in 7.17.2.