Only apply non-null Groovy Template properties

Previously, properties were always applied even when they had a null
value. When using the property defaults, this would leave the
GroovyMarkupConfigurer bean with null values for autoIndentString,
locale, and newLineString. The null values could cause problems at
runtime, for example an NPE when Groovy Templates tries to call
toString on the null newLineString.

Closes gh-47139

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/groovy/template/GroovyTemplateAutoConfiguration.java

@@ -115,7 +115,7 @@ public class GroovyTemplateAutoConfiguration {
 		GroovyMarkupConfigurer groovyMarkupConfigurer(ObjectProvider<MarkupTemplateEngine> templateEngine,
 				Environment environment) {
 			GroovyMarkupConfigurer configurer = new GroovyMarkupConfigurer();
-			PropertyMapper map = PropertyMapper.get();
+			PropertyMapper map = PropertyMapper.get().alwaysApplyingWhenNonNull();
 			map.from(this.properties::isAutoEscape).to(configurer::setAutoEscape);
 			map.from(this.properties::isAutoIndent).to(configurer::setAutoIndent);
 			map.from(this.properties::getAutoIndentString).to(configurer::setAutoIndentString);

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/groovy/template/GroovyTemplateAutoConfigurationTests.java

@@ -25,6 +25,7 @@ import java.util.Locale;
 import java.util.Map;
 
 import groovy.text.markup.BaseTemplate;
+import groovy.text.markup.DelegatingIndentWriter;
 import groovy.text.markup.MarkupTemplateEngine;
 import groovy.text.markup.TemplateConfiguration;
 import jakarta.servlet.http.HttpServletRequest;
@@ -159,9 +160,16 @@ class GroovyTemplateAutoConfigurationTests {
 		assertThat(result).contains("suffixed");
 	}
 
+	@Test
+	void defaultResourceLoaderPath() throws Exception {
+		registerAndRefreshContext();
+		assertThat(this.context.getBean(GroovyMarkupConfigurer.class).getResourceLoaderPath())
+			.isEqualTo(GroovyTemplateProperties.DEFAULT_RESOURCE_LOADER_PATH);
+	}
+
 	@Test
 	@WithResource(name = "custom-templates/custom.tpl", content = "yield \"custom\"")
-	void customTemplateLoaderPath() throws Exception {
+	void customResourceLoaderPath() throws Exception {
 		registerAndRefreshContext("spring.groovy.template.resource-loader-path:classpath:/custom-templates/");
 		MockHttpServletResponse response = render("custom");
 		String result = response.getContentAsString();
@@ -206,6 +214,13 @@ class GroovyTemplateAutoConfigurationTests {
 		assertThat(this.context.getBean(GroovyMarkupConfigurer.class).isAutoIndent()).isTrue();
 	}
 
+	@Test
+	void defaultAutoIndentString() {
+		registerAndRefreshContext();
+		assertThat(this.context.getBean(GroovyMarkupConfigurer.class).getAutoIndentString())
+			.isEqualTo(DelegatingIndentWriter.SPACES);
+	}
+
 	@Test
 	void customAutoIndentString() {
 		registerAndRefreshContext("spring.groovy.template.auto-indent-string:\\t");
@@ -218,6 +233,13 @@ class GroovyTemplateAutoConfigurationTests {
 		assertThat(this.context.getBean(GroovyMarkupConfigurer.class).isAutoNewLine()).isTrue();
 	}
 
+	@Test
+	void defaultBaseTemplateClass() {
+		registerAndRefreshContext();
+		assertThat(this.context.getBean(GroovyMarkupConfigurer.class).getBaseTemplateClass())
+			.isEqualTo(BaseTemplate.class);
+	}
+
 	@Test
 	void customBaseTemplateClass() {
 		registerAndRefreshContext("spring.groovy.template.base-template-class:" + CustomBaseTemplate.class.getName());
@@ -225,6 +247,12 @@ class GroovyTemplateAutoConfigurationTests {
 			.isEqualTo(CustomBaseTemplate.class);
 	}
 
+	@Test
+	void defaultDeclarationEncoding() {
+		registerAndRefreshContext();
+		assertThat(this.context.getBean(GroovyMarkupConfigurer.class).getDeclarationEncoding()).isNull();
+	}
+
 	@Test
 	void customDeclarationEncoding() {
 		registerAndRefreshContext("spring.groovy.template.declaration-encoding:UTF-8");
@@ -237,12 +265,25 @@ class GroovyTemplateAutoConfigurationTests {
 		assertThat(this.context.getBean(GroovyMarkupConfigurer.class).isExpandEmptyElements()).isTrue();
 	}
 
+	@Test
+	void defaultLocale() {
+		registerAndRefreshContext();
+		assertThat(this.context.getBean(GroovyMarkupConfigurer.class).getLocale()).isEqualTo(Locale.getDefault());
+	}
+
 	@Test
 	void customLocale() {
 		registerAndRefreshContext("spring.groovy.template.locale:en_US");
 		assertThat(this.context.getBean(GroovyMarkupConfigurer.class).getLocale()).isEqualTo(Locale.US);
 	}
 
+	@Test
+	void defaultNewLineString() {
+		registerAndRefreshContext();
+		assertThat(this.context.getBean(GroovyMarkupConfigurer.class).getNewLineString())
+			.isEqualTo(System.lineSeparator());
+	}
+
 	@Test
 	void customNewLineString() {
 		registerAndRefreshContext("spring.groovy.template.new-line-string:\\r\\n");