Support configuration of defaultValue and emptyStringIsFalse

This commit adds support for configuring defaultValue and
emptyStringIsFalse to MustacheCompilerFactoryBean.

Closes gh-4057

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/mustache/MustacheCompilerFactoryBean.java

@@ -48,6 +48,10 @@ public class MustacheCompilerFactoryBean implements FactoryBean<Mustache.Compile
 
 	private Compiler compiler;
 
+	private String defaultValue;
+
+	private Boolean emptyStringIsFalse;
+
 	public void setDelims(String delims) {
 		this.delims = delims;
 	}
@@ -68,6 +72,14 @@ public class MustacheCompilerFactoryBean implements FactoryBean<Mustache.Compile
 		this.collector = collector;
 	}
 
+	public void setDefaultValue(String defaultValue) {
+		this.defaultValue = defaultValue;
+	}
+
+	public void setEmptyStringIsFalse(Boolean emptyStringIsFalse) {
+		this.emptyStringIsFalse = emptyStringIsFalse;
+	}
+
 	@Override
 	public Mustache.Compiler getObject() throws Exception {
 		this.compiler = Mustache.compiler();
@@ -86,6 +98,12 @@ public class MustacheCompilerFactoryBean implements FactoryBean<Mustache.Compile
 		if (this.collector != null) {
 			this.compiler = this.compiler.withCollector(this.collector);
 		}
+		if (this.defaultValue != null) {
+		this.compiler = this.compiler.defaultValue(this.defaultValue);
+		}
+		if (this.emptyStringIsFalse != null) {
+		this.compiler = this.compiler.emptyStringIsFalse(this.emptyStringIsFalse);
+		}
 		return this.compiler;
 	}