feat(flagd): log error on invalid env var parsing

[buildingisfun23]

Summary

• Adds ERROR-level log output when environment variables cannot be parsed, instead of silently falling back to defaults
• Covers integer, long, and list parsing in Config.java
• Uses the existing @Slf4j logger already present on the class

Fixes #1673

[gemini-code-assist]

Code Review

This pull request introduces error logging to the environment variable fallback methods in the Config class to improve observability when parsing fails. The review feedback suggests including the caught exception in the log.error calls to capture stack traces for better debugging and recommends caching the environment variable value to avoid redundant System.getenv calls.

[gemini-code-assist]

It is recommended to include the exception e in the log.error call. This allows the logger to capture the stack trace and the specific error message (e.g., why the integer parsing failed), which is invaluable for debugging. Additionally, note that System.getenv(key) is called multiple times in this method; while not a performance bottleneck in a configuration loader, it is generally better practice to retrieve the value once to ensure consistency and avoid redundant system lookups.

Suggested change

	log.error(
	"Failed to parse env variable '{}' with value '{}' as int, using default: {}",
	key,
	System.getenv(key),
	defaultValue);
	log.error(
	"Failed to parse env variable '{}' with value '{}' as int, using default: {}",
	key,
	System.getenv(key),
	defaultValue,
	e);

[gemini-code-assist]

Including the exception e in the log output provides the root cause of the parsing failure, which aids in troubleshooting. Also, consider capturing the result of System.getenv(key) in a variable at the start of the method to avoid redundant calls and potential (though unlikely) consistency issues if the environment were to change between calls.

Suggested change

	log.error(
	"Failed to parse env variable '{}' with value '{}' as long, using default: {}",
	key,
	System.getenv(key),
	defaultValue);
	log.error(
	"Failed to parse env variable '{}' with value '{}' as long, using default: {}",
	key,
	System.getenv(key),
	defaultValue,
	e);

[gemini-code-assist]

Adding the exception e to the log call ensures that any unexpected errors during the stream processing or splitting are properly documented with a stack trace. As with the other fallback methods, retrieving the environment variable once and reusing it would be more efficient and robust than multiple System.getenv(key) calls.

Suggested change

	log.error(
	"Failed to parse env variable '{}' with value '{}' as list, using default: {}",
	key,
	System.getenv(key),
	defaultValue);
	log.error(
	"Failed to parse env variable '{}' with value '{}' as list, using default: {}",
	key,
	System.getenv(key),
	defaultValue,
	e);