Hide application name placeholder when include property is false

Update log4j configuration so that an empty value is used when
`LOGGED_APPLICATION_NAME` is missing. Prior to this commit when
`logging.include-application-name` was `false` the logged output
would include the raw `${sys:LOGGED_APPLICATION_NAME}` value.

See gh-38847

Author: Iliès BELDJILALI

spring-boot-project/spring-boot/src/main/resources/org/springframework/boot/logging/log4j2/log4j2-file.xml

@@ -5,7 +5,7 @@
 		<Property name="LOG_LEVEL_PATTERN">%5p</Property>
 		<Property name="LOG_DATEFORMAT_PATTERN">yyyy-MM-dd'T'HH:mm:ss.SSSXXX</Property>
 		<Property name="CONSOLE_LOG_PATTERN">%clr{%d{${sys:LOG_DATEFORMAT_PATTERN}}}{faint} %clr{${sys:LOG_LEVEL_PATTERN}} %clr{%pid}{magenta} %clr{---}{faint} %clr{${sys:LOGGED_APPLICATION_NAME:-}[%15.15t]}{faint} %clr{${sys:LOG_CORRELATION_PATTERN:-}}{faint}%clr{%-40.40c{1.}}{cyan} %clr{:}{faint} %m%n${sys:LOG_EXCEPTION_CONVERSION_WORD}</Property>
-		<Property name="FILE_LOG_PATTERN">%d{${sys:LOG_DATEFORMAT_PATTERN}} ${sys:LOG_LEVEL_PATTERN} %pid --- ${sys:LOGGED_APPLICATION_NAME}[%t] ${sys:LOG_CORRELATION_PATTERN:-}%-40.40c{1.} : %m%n${sys:LOG_EXCEPTION_CONVERSION_WORD}</Property>
+		<Property name="FILE_LOG_PATTERN">%d{${sys:LOG_DATEFORMAT_PATTERN}} ${sys:LOG_LEVEL_PATTERN} %pid --- ${sys:LOGGED_APPLICATION_NAME:-}[%t] ${sys:LOG_CORRELATION_PATTERN:-}%-40.40c{1.} : %m%n${sys:LOG_EXCEPTION_CONVERSION_WORD}</Property>
 	</Properties>
 	<Appenders>
 		<Console name="Console" target="SYSTEM_OUT" follow="true">

spring-boot-project/spring-boot/src/main/resources/org/springframework/boot/logging/log4j2/log4j2.xml

@@ -4,8 +4,8 @@
 		<Property name="LOG_EXCEPTION_CONVERSION_WORD">%xwEx</Property>
 		<Property name="LOG_LEVEL_PATTERN">%5p</Property>
 		<Property name="LOG_DATEFORMAT_PATTERN">yyyy-MM-dd'T'HH:mm:ss.SSSXXX</Property>
-		<Property name="CONSOLE_LOG_PATTERN">%clr{%d{${sys:LOG_DATEFORMAT_PATTERN}}}{faint} %clr{${sys:LOG_LEVEL_PATTERN}} %clr{%pid}{magenta} %clr{---}{faint} %clr{${sys:LOGGED_APPLICATION_NAME}[%15.15t]}{faint} %clr{${sys:LOG_CORRELATION_PATTERN:-}}{faint}%clr{%-40.40c{1.}}{cyan} %clr{:}{faint} %m%n${sys:LOG_EXCEPTION_CONVERSION_WORD}</Property>
-		<Property name="FILE_LOG_PATTERN">%d{${sys:LOG_DATEFORMAT_PATTERN}} ${sys:LOG_LEVEL_PATTERN} %pid --- ${sys:LOGGED_APPLICATION_NAME}[%t] ${sys:LOG_CORRELATION_PATTERN:-}%-40.40c{1.} : %m%n${sys:LOG_EXCEPTION_CONVERSION_WORD}</Property>
+		<Property name="CONSOLE_LOG_PATTERN">%clr{%d{${sys:LOG_DATEFORMAT_PATTERN}}}{faint} %clr{${sys:LOG_LEVEL_PATTERN}} %clr{%pid}{magenta} %clr{---}{faint} %clr{${sys:LOGGED_APPLICATION_NAME:-}[%15.15t]}{faint} %clr{${sys:LOG_CORRELATION_PATTERN:-}}{faint}%clr{%-40.40c{1.}}{cyan} %clr{:}{faint} %m%n${sys:LOG_EXCEPTION_CONVERSION_WORD}</Property>
+		<Property name="FILE_LOG_PATTERN">%d{${sys:LOG_DATEFORMAT_PATTERN}} ${sys:LOG_LEVEL_PATTERN} %pid --- ${sys:LOGGED_APPLICATION_NAME:-}[%t] ${sys:LOG_CORRELATION_PATTERN:-}%-40.40c{1.} : %m%n${sys:LOG_EXCEPTION_CONVERSION_WORD}</Property>
 	</Properties>
 	<Appenders>
 		<Console name="Console" target="SYSTEM_OUT" follow="true">

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/logging/log4j2/Log4J2LoggingSystemTests.java

@@ -574,6 +574,17 @@ void applicationNameLoggingWhenHasApplicationName(CapturedOutput output) {
 		assertThat(getLineWithText(output, "Hello world")).contains("[myapp] ");
 	}
 
+	@Test
+	void applicationNamePlaceHolderNotShowingWhenDisabled(CapturedOutput output) {
+		this.environment.setProperty("spring.application.name", "application-name");
+		this.environment.setProperty("logging.include-application-name", "false");
+		this.loggingSystem.setStandardConfigLocations(false);
+		this.loggingSystem.beforeInitialize();
+		this.loggingSystem.initialize(this.initializationContext, null, null);
+		this.logger.info("Hello world");
+		assertThat(getLineWithText(output, "Hello world")).doesNotContain("${sys:LOGGED_APPLICATION_NAME}");
+	}
+
 	@Test
 	void applicationNameLoggingWhenDisabled(CapturedOutput output) {
 		this.environment.setProperty("spring.application.name", "myapp");