chore: fail with clear error when script EIP has empty expression body

[davsclaus]

Summary

Claude Code on behalf of Claus Ibsen

When camel-xml-io-dsl parses a whitespace-only expression body (e.g., <groovy>\n</groovy>), the expression text ends up as null. At runtime, GroovyLanguage.getScriptFromCache(null) calls ConcurrentHashMap.get(null), which throws an unhelpful NullPointerException.

This PR adds validation in ScriptReifier.createProcessor() to detect null/empty script code early and throw a clear IllegalArgumentException with the message: "Script has no script code configured in ..."

This is the intended behavior — an empty tag is regarded as null by camel-xml-io-dsl (by design), but the NPE error message was confusing.

Reported on Zulip: https://camel.zulipchat.com/#narrow/channel/257298-camel/topic/camel-xml-io.20drops.20whitespace-only.20expression.20bodies

Changes

• core/camel-core-reifier/src/main/java/org/apache/camel/reifier/ScriptReifier.java — Added null/empty check on the expression definition before creating the runtime expression and processor

Test plan

• Full reactor build passes (mvn clean install -DskipTests)
• Code formatting verified (mvn formatter:format impsort:sort)
• Verify with a route containing <groovy></groovy> that the error message is clear instead of NPE

🤖 Generated with Claude Code

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🧪 CI tested the following changed modules:

• core/camel-core-reifier

ℹ️ Dependent modules were not tested because the total number of affected modules exceeded the threshold (50). Use the test-dependents label to force testing all dependents.

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