Possible NPE in Spring MVC LogFormatUtils

[gonzalad]

Affects: 5.2.15

When using Spring Boot (2.3.12) and when I activate debug: true in application.yml, I can get a NullPointerException thrown by LogFormatUtils.formatValue(LogFormatUtils.java:62).

Sample stacktrace:

java.lang.NullPointerException: null
    at org.springframework.core.log.LogFormatUtils.formatValue(LogFormatUtils.java:62)
    at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.lambda$writeWithMessageConverters$0(AbstractMessageConverterMethodProcessor.java:274)
    at org.springframework.core.log.LogFormatUtils.traceDebug(LogFormatUtils.java:86)
    at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:273)
    at org.springframework.web.servlet.mvc.method.annotation.HttpEntityMethodProcessor.handleReturnValue(HttpEntityMethodProcessor.java:219)
    at org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue(HandlerMethodReturnValueHandlerComposite.java:82)
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:123)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:878)
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:792)
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1040)

Looking at the code of LogFormatUtils, the error can happen if value.toString() returns null.
Which is the case in my situation (value is an instance if InMemoryResource in my sample)

	public static String formatValue(@Nullable Object value, boolean limitLength) {
		if (value == null) {
			return "";
		}
		String str;
		if (value instanceof CharSequence) {
			str = "\"" + value + "\"";
		}
		else {
			try {
				str = value.toString();
			}
			catch (Throwable ex) {
				str = ex.toString();
			}
		}
		return (limitLength && str.length() > 100 ? str.substring(0, 100) + " (truncated)..." : str);
	}