perf: reduce garbage from validators when we create empty strings while we can use null value instead.

No functional changes.

Author: php-coder

src/main/java/ru/mystamps/web/support/beanvalidation/FieldsMatchValidator.java

@@ -46,13 +46,13 @@ public boolean isValid(Object value, ConstraintValidatorContext ctx) {
 		PropertyAccessor bean = new BeanWrapperImpl(value);
 
 		Object firstField      = bean.getPropertyValue(firstFieldName);
-		String firstFieldValue = Objects.toString(firstField, "");
+		String firstFieldValue = Objects.toString(firstField, null);
 		if (StringUtils.isEmpty(firstFieldValue)) {
 			return true;
 		}
 
 		Object secondField      = bean.getPropertyValue(secondFieldName);
-		String secondFieldValue = Objects.toString(secondField, "");
+		String secondFieldValue = Objects.toString(secondField, null);
 		if (StringUtils.isEmpty(secondFieldValue)) {
 			return true;
 		}

src/main/java/ru/mystamps/web/support/beanvalidation/FieldsMismatchValidator.java

@@ -46,13 +46,13 @@ public boolean isValid(Object value, ConstraintValidatorContext ctx) {
 		PropertyAccessor bean = new BeanWrapperImpl(value);
 
 		Object firstField      = bean.getPropertyValue(firstFieldName);
-		String firstFieldValue = Objects.toString(firstField, "");
+		String firstFieldValue = Objects.toString(firstField, null);
 		if (StringUtils.isEmpty(firstFieldValue)) {
 			return true;
 		}
 
 		Object secondField      = bean.getPropertyValue(secondFieldName);
-		String secondFieldValue = Objects.toString(secondField, "");
+		String secondFieldValue = Objects.toString(secondField, null);
 		if (StringUtils.isEmpty(secondFieldValue)) {
 			return true;
 		}

src/main/java/ru/mystamps/web/support/beanvalidation/NotNullIfFirstFieldValidator.java

@@ -47,13 +47,13 @@ public boolean isValid(Object value, ConstraintValidatorContext ctx) {
 		PropertyAccessor bean = new BeanWrapperImpl(value);
 
 		Object firstField      = bean.getPropertyValue(firstFieldName);
-		String firstFieldValue = Objects.toString(firstField, "");
+		String firstFieldValue = Objects.toString(firstField, null);
 		if (StringUtils.isEmpty(firstFieldValue)) {
 			return true;
 		}
 
 		Object secondField      = bean.getPropertyValue(secondFieldName);
-		String secondFieldValue = Objects.toString(secondField, "");
+		String secondFieldValue = Objects.toString(secondField, null);
 		if (StringUtils.isNotEmpty(secondFieldValue)) {
 			return true;
 		}