Add a sample for joining multiple streams into a pipeline.

I am running the steams example from > Labs > Streams: Aggregate and I am curious about the expected behaviour when using a SUM style aggregate approach.

When I run the application from the example code it is working all fine and I can see the correct responses that at every 5000 ms it produces the correct response. However if I leave the app running and don't inject any messages I get no message at all. It seems the absence of invoking the http request does not create a result of zero. Can you confirm this is expected?

If it is expected what would be the recommend means for me to send to a downstream system that the result of 0 messages is 0 messages received. I am asking because in my use case I want to create a stream of data that I am using to track items and display the amount of items currently being tracked. However there will be times when there are 0 messages received in the time window. I need a way to notify downstream that I am still tracking but currently there are no items being tracked.

For example:
Time window 1: 1000 messages from 5 unique items = Result 5 Items being tracked
Time window 2: 1500 messages from 5 unique items = Still result 5 Items being tracked
Time window 3: 0 messages received so no unique items --> Currently no message. Therefore am I still tracking 5 or 0 items.

I need a way for a sum result to be available even if I receive no messages.

The version of the demo that I was using that now drives my question is detailed below:

"name": "aggregator",
"type": "flogo:app",
"version": "0.0.1",
"appModel": "1.0.0",

Can we have some examples on how to use all the features of this project in go code?

Hello, when I run the command "flogo create -f agg-flogo.json myApp" on Ubuntu, it shows:

Creating initial project structure, this might take a few seconds ...
all dirs contained build errors
FATAL: command "create" failed: exit status 1

flogo build error
flogo/core version: v1.6.4

detail：
`

warn: [18:02:24.196] command exited with code 1: flogo build
error: [18:02:24.197] undefined
Error building project: # github.com/project-flogo/flow/definition
/root/gopath/pkg/mod/github.com/project-flogo/[email protected]/definition/definition_ser.go:237:32: cannot use ctx (type *initCtxImpl) as type activity.InitContext in argument to f:
*initCtxImpl does not implement activity.InitContext (missing Name method)
github.com/project-flogo/stream/pipeline
/root/gopath/pkg/mod/github.com/project-flogo/[email protected]/pipeline/stage.go:80:90: config.Operation undefined (type *StageConfig has no field or method Operation)
/root/gopath/pkg/mod/github.com/project-flogo/[email protected]/pipeline/stage.go:81:15: cannot use initCtx (type *initContextImpl) as type activity.InitContext in argument to f:
*initContextImpl does not implement activity.InitContext (missing Name method)

`

Current behavior (how does the issue manifest):
Running flogo-cli to build example fails with error

Expected behavior:
Build should generate app
Minimal steps to reproduce the problem (not required if feature enhancement):

$ flogo create -f agg-flogo.json
Creating initial project structure, this might take a few seconds ...
$ cd stream
$ flogo prepare
$ flogo build

stream/vendor/github.com/project-flogo/stream/pipeline

vendor/github.com/project-flogo/stream/pipeline/instance.go:21:13: undefined: channels.Channel
FATAL: command "build" failed: exit status 2

Please tell us about your environment (Operating system, docker version, browser & web ui version, etc):

Flogo version (CLI & contrib/lib. If unknown, leave empty or state unknown): 0.X.X
Performed update from GitHub today (26-Sep) of flogo-cli, flogo-contrib, and flogs-lib

Additional information you deem important (e.g. issue happens only occasionally):