HV-1623 Replace empty check in Contracts with null and empty check at the same time

- based on our usage of not empty check passed parameters should not be null as well hence the implementation of the check can use StringHelper.isNullOrEmptyString utility method.

Author: marko-bekhta

engine/src/main/java/org/hibernate/validator/internal/cfg/context/TypeConstraintMappingContextImpl.java

@@ -134,7 +134,6 @@ public PropertyConstraintMappingContext property(String property, ElementType el
 
 	@Override
 	public PropertyConstraintMappingContext field(String property) {
-		Contracts.assertNotNull( property, "The property name must not be null." );
 		Contracts.assertNotEmpty( property, MESSAGES.propertyNameMustNotBeEmpty() );
 
 		JavaBeanField javaBeanField = getFieldProperty( beanClass, property );
@@ -155,7 +154,6 @@ public PropertyConstraintMappingContext field(String property) {
 
 	@Override
 	public PropertyConstraintMappingContext getter(String property) {
-		Contracts.assertNotNull( property, "The property name must not be null." );
 		Contracts.assertNotEmpty( property, MESSAGES.propertyNameMustNotBeEmpty() );
 
 		JavaBeanGetter javaBeanGetter = getGetterProperty( beanClass, property );

engine/src/main/java/org/hibernate/validator/internal/util/Contracts.java

@@ -75,7 +75,7 @@ public static void assertTrue(boolean condition, String message, Object... messa
 	}
 
 	public static void assertNotEmpty(String s, String message) {
-		if ( s.length() == 0 ) {
+		if ( StringHelper.isNullOrEmptyString( s ) ) {
 			throw LOG.getIllegalArgumentException( message );
 		}
 	}