FIX: null certificate value should be valid in opensearch connection (o…

…pensearch-project#4494)

* FIX: null certificate value should be valid

Signed-off-by: George Chen <qchea@amazon.com>

data-prepper-plugins/opensearch/src/main/java/org/opensearch/dataprepper/plugins/source/opensearch/configuration/ConnectionConfiguration.java

@@ -12,6 +12,7 @@
 import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.time.Duration;
+import java.util.Objects;
 
 public class ConnectionConfiguration {
 
@@ -62,7 +63,7 @@ boolean certificateFileAndContentAreMutuallyExclusive() {
 
   @AssertTrue(message = "certificate must be either valid PEM file path or public key content.")
   boolean isCertificateValid() {
-    if (PemObjectValidator.isPemObject(certificate)) {
+    if (Objects.isNull(certificate) || PemObjectValidator.isPemObject(certificate)) {
       return true;
     }
     try {

data-prepper-plugins/opensearch/src/test/java/org/opensearch/dataprepper/plugins/source/opensearch/configuration/ConnectionConfigurationTest.java

@@ -62,6 +62,7 @@ void connection_configuration_values_test() throws JsonProcessingException {
         assertThat(connectionConfig.getSocketTimeout(),equalTo(null));
         assertThat(connectionConfig.getConnectTimeout(),equalTo(null));
         assertThat(connectionConfig.isInsecure(),equalTo(true));
+        assertThat(connectionConfig.isCertificateValid(), is(true));
     }
 
     @ParameterizedTest