Backend crashes if trying to refresh previously non-existent Canvas cache

[michaelgira23]

I clicked "Refresh Canvas Feed" button on planner, and got this error:

/Users/michaelgira/Desktop/MyMICDS-v2/node_modules/mongodb/lib/utils.js:123
    process.nextTick(function() { throw err; });
                                  ^

TypeError: Cannot read property 'forEach' of null
    at canvasdata.deleteMany.err (/Users/michaelgira/Desktop/MyMICDS-v2/src/libs/feeds.js:57:12)
    at /Users/michaelgira/Desktop/MyMICDS-v2/node_modules/mongodb/lib/collection.js:1215:18
    at handleCallback (/Users/michaelgira/Desktop/MyMICDS-v2/node_modules/mongodb/lib/utils.js:120:56)
    at /Users/michaelgira/Desktop/MyMICDS-v2/node_modules/mongodb/lib/collection.js:1252:5
    at /Users/michaelgira/Desktop/MyMICDS-v2/node_modules/mongodb-core/lib/connection/pool.js:469:18
    at process._tickCallback (internal/process/next_tick.js:150:11)