Java - Type cast null parameters in samples and tests - #11967

Updates Java emitter example generation so typed null arguments avoid ambiguous overloaded calls.

Changes:

• Added shared null-parameter casting logic.
• Applied it to protocol and client-method examples.
• Updated generated samples/tests and added coverage plus a changelog entry.

Suppressed comments (2)

packages/http-client-java/generator/http-client-generator-core/src/main/java/com/microsoft/typespec/http/client/generator/core/template/example/ClientMethodExampleWriter.java:67

• The added tests do not exercise this ClientMethodExampleWriter path; they only call ExampleWriterUtil.getParameterExpression directly. Add an entrypoint test for a client-method example with a typed null parameter so the parameter mapping, cast, and required import are verified together.

        String parameterInvocations = methodParameters.stream()
            .map(methodParameter -> ExampleWriterUtil.getParameterExpression(
                methodParameter.getClientMethodParameter().getClientType(),
                nodeVisitor.accept(parseNodeFromParameter(method, proxyMethodExample, methodParameter))))
            .collect(Collectors.joining(", "));

packages/http-client-java/generator/http-client-generator-core/src/main/java/com/microsoft/typespec/http/client/generator/core/template/example/ProtocolExampleWriter.java:82

• This new call site is not covered by the added tests: ExampleWriterUtilTests invokes the helper directly, so it would still pass if ProtocolExampleWriter stopped applying the cast or collecting the type import. Add a template/writer test that exercises a nullable non-java.lang parameter (for example OffsetDateTime) and asserts the rendered invocation and imports.

            params.add(ExampleWriterUtil.getParameterExpression(parameter.getClientType(),
                parameter.getClientType().defaultValueExpression()));

• Files reviewed: 5/15 changed files
• Comments generated: 1
• Review effort level: Lite