[license] Handle missing composer license without TypeError

[coisa]

Problem

Installing or running DevTools inside the composer-plugin consumer fixture exposed a fatal error in the LICENSE generation flow when the consumer composer.json does not declare a license field:

In Resolver.php line 54:

  [TypeError]
  FastForward\DevTools\License\Resolver::resolve(): Argument #1 ($license) must be of type string, null given, called in /Users/mentordosnerds/Sites/github.com/php-fast-forward/dev-tools/src/License/Generator.php on line 87

Generator::generateContent() passes ComposerJsonInterface::getLicense() directly into ResolverInterface::resolve(). The resolver requires a non-null string, so repositories without a license field crash before the generator can follow its documented “unsupported or unavailable license returns null” behavior.

Expected Behavior

A missing license in the consumer composer.json MUST be handled as a non-generatable LICENSE state, not as a fatal TypeError.

The license command and any sync/install flow that triggers LICENSE generation SHOULD:

• return null / skip generation when composer.json has no license field;
• avoid writing a LICENSE file when no supported license can be resolved;
• emit clear command feedback when the command surface needs to explain why generation was skipped;
• preserve the current behavior for supported and unsupported non-null license strings.

Implementation Notes

Likely areas to inspect:

• src/License/Generator.php
• src/License/Resolver.php
• src/License/ResolverInterface.php
• src/Console/Command/LicenseCommand.php
• tests/License/GeneratorTest.php
• tests/License/ResolverTest.php
• tests/Console/Command/LicenseCommandTest.php
• tests/Fixtures/composer-plugin-consumer/composer.json

Possible approaches:

• Guard Generator::generateContent() before calling the resolver when ComposerJsonInterface::getLicense() returns null or an empty string.
• Alternatively, update the resolver contract to accept ?string and normalize missing/empty values to null resolution.

The implementation SHOULD choose the contract that keeps responsibilities clearest and avoids spreading null checks across command orchestration.

Acceptance Criteria

• A consumer project without license in composer.json no longer crashes when composer dev-tools license or the relevant sync/install flow runs.
• Missing or empty license metadata produces no LICENSE output and returns a controlled skip/null result.
• Unsupported string license identifiers still return a controlled skip/null result.
• Supported license identifiers continue generating the expected content.
• PHPUnit coverage includes at least one missing-license regression case.
• The composer-plugin consumer fixture can be used to reproduce the no-license path without a fatal TypeError.
• CHANGELOG.md documents the bug fix.

Non-Goals

• Do not infer a default license for consumers.
• Do not change supported license template mappings unless needed for this bug.
• Do not broaden this issue into a full license metadata redesign.