Cast to ObjectId failed for value "5f1db..." at path "_id" for model "Agent"

    CastError: Cast to ObjectId failed for value "5f1db..." at path "_id" for model "Agent"
    at new CastError (/var/app/current/node_modules/mongoose/lib/error/cast.js:29:11)
    at ObjectId.cast (/var/app/current/node_modules/mongoose/lib/schema/objectid.js:246:11)
    at ObjectId.SchemaType.applySetters (/var/app/current/node_modules/mongoose/lib/schematype.js:969:12)
    at ObjectId.SchemaType._castForQuery (/var/app/current/node_modules/mongoose/lib/schematype.js:1383:15)
    at ObjectId.SchemaType.castForQuery (/var/app/current/node_modules/mongoose/lib/schematype.js:1373:15)
    at ObjectId.SchemaType.castForQueryWrapper (/var/app/current/node_modules/mongoose/lib/schematype.js:1352:15)
    at cast (/var/app/current/node_modules/mongoose/lib/cast.js:315:32)
    at model.Query.Query.cast (/var/app/current/node_modules/mongoose/lib/query.js:4644:12)
    at model.Query.Query._castConditions (/var/app/current/node_modules/mongoose/lib/query.js:1842:10)
    at model.Query.<anonymous> (/var/app/current/node_modules/mongoose/lib/query.js:2097:8)
    at model.Query._wrappedThunk [as _findOne] (/var/app/current/node_modules/mongoose/lib/helpers/query/wrapThunk.js:16:8)
    at process.nextTick (/var/app/current/node_modules/kareem/index.js:369:33)
    at Shim.applySegment (/var/app/current/node_modules/newrelic/lib/shim/shim.js:1425:20)
    at wrapper (/var/app/current/node_modules/newrelic/lib/shim/shim.js:2087:17)
    at process._tickCallback (internal/process/next_tick.js:61:11)