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From "ASF GitHub Bot (JIRA)" <>
Subject [jira] [Commented] (BEAM-440) Create.values() returns a type-unsafe Coder
Date Wed, 17 Aug 2016 21:55:20 GMT


ASF GitHub Bot commented on BEAM-440:

GitHub user JasonMWhite opened a pull request:

    [BEAM-440] add Create#empty

    Be sure to do all of the following to help us incorporate your contribution
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You can merge this pull request into a Git repository by running:

    $ git pull create_empty

Alternatively you can review and apply these changes as the patch at:

To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:

    This closes #843
commit d38b30204d1201b9146dd69bd312ec066314912d
Author: Jason White <>
Date:   2016-08-16T23:35:47Z

    add Create#empty


> Create.values() returns a type-unsafe Coder
> -------------------------------------------
>                 Key: BEAM-440
>                 URL:
>             Project: Beam
>          Issue Type: Bug
>          Components: sdk-java-core
>            Reporter: Daniel Halperin
>              Labels: newbie, starter
> Create.values() with no arguments will default to a VoidCoder, unless one is set later
with #setCoder(Coder).
> Although it will encode its input correctly, this seems like a bad choice in many cases.
E.g., with Flatten:
>     PCollection<KV<SomeClass, Integer>> initial = p.apply("First", Create.<KV<SomeClass,
>     PCollection<KV<SomeClass, Integer>> second =
>         p.apply("Second", Create.of("a", "b")).apply(ParDo.of(new MyAvroDoFn()));
>     PCollectionList
>     .of(initial).and(second)
>         .apply(Flatten.<KV<SomeClass, Integer>>pCollections());
> This crashes trying to cast a KV from "Second" to a Void.class.
> 1. Suggest throwing a warning in #getDefaultOutputCoder when defaulting to VoidCoder
for an empty elements list. Should this be an error?
> 2. Suggest adding something like Create.empty(TypeDescriptor) to handle this case properly.

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