updating to keep java 8 compatibility

Author: jorgesartori

src/main/java/com/networknt/schema/ReadOnlyValidator.java

@@ -16,6 +16,7 @@
 
 package com.networknt.schema;
 
+import java.util.HashSet;
 import java.util.Set;
 
 import org.slf4j.Logger;
@@ -39,11 +40,11 @@ public ReadOnlyValidator(String schemaPath, JsonNode schemaNode, JsonSchema pare
 
     public Set<ValidationMessage> validate(JsonNode node, JsonNode rootNode, String at) {
         debug(logger, node, rootNode, at);
+        Set<ValidationMessage> errors= new HashSet<ValidationMessage>();
         if (writeMode) {
-            return Set.of(buildValidationMessage(at));
-        } else {
-            return Set.of();
-        }
+        	errors.add(buildValidationMessage(at));
+        } 
+        return errors;
     }
 
 }

src/test/java/com/networknt/schema/ReadOnlyValidatorTest.java

@@ -7,6 +7,7 @@
 import java.io.IOException;
 import java.io.InputStream;
 import java.util.Set;
+import java.util.stream.Collectors;
 
 import org.junit.jupiter.api.Test;
 
@@ -28,7 +29,7 @@ void givenConfigWriteTrueWhenReadOnlyTrueThenDenies() throws IOException {
 		Set<ValidationMessage> errors = loadJsonSchema(true).validate(node);
 		assertFalse(errors.isEmpty());
 		assertEquals("$.firstName: is a readonly field, it cannot be changed",
-				errors.stream().map(e -> e.getMessage()).toList().get(0));
+				errors.stream().map(e -> e.getMessage()).collect(Collectors.toList()).get(0));
 	}
 
 	private JsonSchema loadJsonSchema(Boolean write) {