Fix InputBuilder lazy initialization to prevent validation errors

[ricardozanini]

Summary

Fixed InputBuilder to use lazy initialization instead of eagerly creating from and schema objects in the constructor.

Problem

When users set only a schema without from, the constructor pre-initialized an empty InputFrom object, causing validation errors at runtime:

"Both object and str are null" (ObjectExpressionFactory.java:40)

Users had to work around this by calling build().setFrom(null) explicitly.

Solution

• Changed constructor to NOT pre-initialize from or schema
• Made all builder methods null-safe (check before use)
• Ensured proper field clearing when switching between string/object variants
• Added schemaAsJsonString() method for JSON string schemas

Testing

• Added 18 comprehensive unit tests for InputBuilder
• All 102 tests in the module pass
• Verified the fix addresses the original issue from the AgenticFlow use case

Changes

• InputBuilder.java: Lazy initialization + null-safe methods
• InputBuilderTest.java: New comprehensive test suite

[ricardozanini]

AI generated the tests and the PR description.

[ricardozanini]

@fjtirado why running mvn clean install locally changed the db files?

[Copilot]

Pull request overview

This PR updates the fluent InputBuilder to avoid constructing invalid Input objects by default, addressing runtime validation errors that occurred when only schema was set (without from). It also adds a new builder method to support inline JSON-schema strings and introduces a comprehensive unit test suite for the builder.

Changes:

• Make InputBuilder lazily initialize from (InputFrom) and schema (SchemaUnion) instead of eagerly creating them in the constructor.
• Add schemaAsJsonString(String) to allow setting an inline schema when the schema is available as a JSON string (distinct from the external-URI schema(String) overload).
• Add a new InputBuilderTest suite covering lazy initialization and field-variant switching behavior.

Reviewed changes

Copilot reviewed 2 out of 6 changed files in this pull request and generated 2 comments.

File	Description
fluent/spec/src/main/java/io/serverlessworkflow/fluent/spec/InputBuilder.java	Removes eager initialization and adds lazy init + schemaAsJsonString() support.
fluent/spec/src/test/java/io/serverlessworkflow/fluent/spec/InputBuilderTest.java	Adds unit tests validating lazy initialization and builder behavior across variants.

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 6 changed files in this pull request and generated 3 comments.

[Copilot]

Pull request overview

Copilot reviewed 2 out of 6 changed files in this pull request and generated 4 comments.

[fjtirado]

These db files I guess were added uinentionally

[ricardozanini]

I asked this to you. They were generated with just mvn clean install. I think there's something wrong there.

[ricardozanini]

In the diff, there's only meta changes - the tests are passing.

[fjtirado]

Yes, I have to take a look, but I think we should not couple it with this PR