[changelog] NPE when generating changelog

[aalmiray]

Task List

• Steps to reproduce provided
• Stacktrace (if present) provided
• Example that reproduces the problem (link to git repository is ideal)
• Full description of the issue provided (see below)

Steps to Reproduce

1. Configure a project with a JAVA_BINARY distribution.
2. Invoke jreleaser changelog

Expected Behaviour

The changelog is generated as expected.

Actual Behaviour

An NPE occurs during checksum validation.

Environment Information

• Operating System: N/A
• JReleaser Version: 0.9.0
• JDK Version: N/A

[INFO]  Validating configuration
[DEBUG]   [validation] project
[DEBUG]   [validation] signing
[DEBUG]   [validation] upload
[DEBUG]   [validation] artifactory
[DEBUG]   [validation] http
[DEBUG]   [validation] s3
[DEBUG]   [validation] release
[DEBUG]   [validation] release.github
java.lang.NullPointerException
	at java.io.StringReader.<init>(StringReader.java:50)
	at org.jreleaser.util.MustacheUtils.applyTemplate(MustacheUtils.java:78)
	at org.jreleaser.model.Checksum.getResolvedName(Checksum.java:52)
	at org.jreleaser.model.Checksum.getResolvedName(Checksum.java:56)
	at org.jreleaser.model.releaser.spi.AbstractReleaserBuilder.configureWith(AbstractReleaserBuilder.java:125)
	at org.jreleaser.engine.release.Releasers.releaserFor(Releasers.java:49)
	at org.jreleaser.engine.context.ContextCreator.create(ContextCreator.java:79)
	at org.jreleaser.cli.AbstractModelCommand.createContext(AbstractModelCommand.java:138)
	at org.jreleaser.cli.AbstractModelCommand.execute(AbstractModelCommand.java:79)
	at org.jreleaser.cli.AbstractCommand.call(AbstractCommand.java:70)
	at org.jreleaser.cli.AbstractModelCommand.call(AbstractModelCommand.java:46)
	at org.jreleaser.cli.AbstractCommand.call(AbstractCommand.java:41)
	at picocli.CommandLine.executeUserObject(CommandLine.java:1953)
	at picocli.CommandLine.access$1300(CommandLine.java:145)
	at picocli.CommandLine$RunLast.executeUserObjectOfLastSubcommandWithSameParent(CommandLine.java:2358)
	at picocli.CommandLine$RunLast.handle(CommandLine.java:2352)
	at picocli.CommandLine$RunLast.handle(CommandLine.java:2314)
	at picocli.CommandLine$AbstractParseResultHandler.execute(CommandLine.java:2179)
	at picocli.CommandLine$RunLast.execute(CommandLine.java:2316)
	at picocli.CommandLine.execute(CommandLine.java:2078)
	at org.jreleaser.cli.Main.execute(Main.java:71)
	at org.jreleaser.cli.Main.run(Main.java:56)
	at org.jreleaser.cli.Main.main(Main.java:47)