NPE in MergeYaml

[Bananeweizen]

What is the smallest, simplest way to reproduce the problem?

Configure the org.openrewrite.yaml.MergeYaml without any of the required parameters (I just copied a list of recipes taken from the discover goal) and run OpenRewrite.

What is the full stack trace of any errors you encountered?

 java.lang.NullPointerException: Cannot invoke "String.getBytes(java.nio.charset.Charset)" because "source" is null
	at org.openrewrite.Parser$Input.lambda$fromString$0(Parser.java:175)
	at org.openrewrite.Parser$Input.getSource(Parser.java:215)
	at org.openrewrite.tree.ParseError.build(ParseError.java:97)
	at org.openrewrite.yaml.YamlParser.lambda$parseInputs$0(YamlParser.java:77)
	at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:197)
	at java.base/java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:179)
	at java.base/java.util.ArrayList$ArrayListSpliterator.tryAdvance(ArrayList.java:1602)
	at java.base/java.util.stream.ReferencePipeline.forEachWithCancel(ReferencePipeline.java:129)
	at java.base/java.util.stream.AbstractPipeline.copyIntoWithCancel(AbstractPipeline.java:527)
	at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:513)
	at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:499)
	at java.base/java.util.stream.FindOps$FindOp.evaluateSequential(FindOps.java:150)
	at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
	at java.base/java.util.stream.ReferencePipeline.findFirst(ReferencePipeline.java:647)
	at org.openrewrite.yaml.MergeYaml.lambda$validate$1(MergeYaml.java:66)
	at org.openrewrite.Validated.test(Validated.java:81)
	at org.openrewrite.yaml.MergeYaml.validate(MergeYaml.java:64)
	at org.openrewrite.Recipe.validate(Recipe.java:383)

Are you interested in contributing a fix to OpenRewrite?