Fix DefaultHttpHeaderMapper for Nullability on CS

Author: artembilan

spring-integration-core/src/main/java/org/springframework/integration/config/ConverterRegistrar.java

@@ -59,8 +59,8 @@ public void setApplicationContext(ApplicationContext applicationContext) throws
 	@Override
 	public void afterPropertiesSet() {
 		ConversionService conversionService = IntegrationUtils.getConversionService(this.applicationContext);
-		if (conversionService instanceof GenericConversionService) {
-			registerConverters((GenericConversionService) conversionService);
+		if (conversionService instanceof GenericConversionService genericConversionService) {
+			registerConverters(genericConversionService);
 		}
 		else {
 			Assert.notNull(conversionService,

spring-integration-http/src/main/java/org/springframework/integration/http/support/DefaultHttpHeaderMapper.java

@@ -47,6 +47,7 @@
 import org.springframework.beans.factory.InitializingBean;
 import org.springframework.core.convert.ConversionService;
 import org.springframework.core.convert.TypeDescriptor;
+import org.springframework.core.convert.support.DefaultConversionService;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpMethod;
 import org.springframework.http.MediaType;
@@ -336,15 +337,19 @@ public void setExcludedInboundStandardResponseHeaderNames(String... excludedInbo
 	/**
 	 * Sets the prefix to use with user-defined (non-standard) headers. The default is an
 	 * empty string.
-	 * @param userDefinedHeaderPrefix The user defined header prefix.
+	 * @param userDefinedHeaderPrefix The user defined the header prefix.
 	 */
 	public void setUserDefinedHeaderPrefix(@Nullable String userDefinedHeaderPrefix) {
 		this.userDefinedHeaderPrefix = (userDefinedHeaderPrefix != null) ? userDefinedHeaderPrefix : "";
 	}
 
 	@Override
 	public void afterPropertiesSet() {
-		this.conversionService = IntegrationUtils.getConversionService(this.beanFactory);
+		ConversionService conversionServiceToUse = IntegrationUtils.getConversionService(this.beanFactory);
+		if (conversionServiceToUse == null) {
+			conversionServiceToUse = DefaultConversionService.getSharedInstance();
+		}
+		this.conversionService = conversionServiceToUse;
 	}
 
 	/**