Use Collections.isEmpty() instead of .size() == 0

Ensure that Collections.isEmpty() is used to check if there are no
elements in a collections. This is more explicit and can be faster than
calling .size().

Closes gh-4783

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/condition/AnyNestedCondition.java

@@ -50,7 +50,7 @@ public abstract class AnyNestedCondition extends AbstractNestedCondition {
 
 	@Override
 	protected ConditionOutcome getFinalMatchOutcome(MemberMatchOutcomes memberOutcomes) {
-		return new ConditionOutcome(memberOutcomes.getMatches().size() > 0,
+		return new ConditionOutcome(!memberOutcomes.getMatches().isEmpty(),
 				"nested any match resulted in " + memberOutcomes.getMatches()
 						+ " matches and " + memberOutcomes.getNonMatches()
 						+ " non matches");

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/condition/OnResourceCondition.java

@@ -47,7 +47,7 @@ class OnResourceCondition extends SpringBootCondition {
 					? this.defaultResourceLoader : context.getResourceLoader();
 			List<String> locations = new ArrayList<String>();
 			collectValues(locations, attributes.get("resources"));
-			Assert.isTrue(locations.size() > 0,
+			Assert.isTrue(!locations.isEmpty(),
 					"@ConditionalOnResource annotations must specify at least one resource location");
 			for (String location : locations) {
 				if (!loader

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/logging/AutoConfigurationReportLoggingInitializer.java

@@ -106,7 +106,7 @@ public class AutoConfigurationReportLoggingInitializer
 			this.report = ConditionEvaluationReport
 					.get(this.applicationContext.getBeanFactory());
 		}
-		if (this.report.getConditionAndOutcomesBySource().size() > 0) {
+		if (!this.report.getConditionAndOutcomesBySource().isEmpty()) {
 			if (isCrashReport && this.logger.isInfoEnabled()
 					&& !this.logger.isDebugEnabled()) {
 				this.logger.info("\n\nError starting ApplicationContext. "