Adding validations to certificate deletion operation

components/certificate-mgt/org.wso2.carbon.certificate.mgt.cert.admin.api/src/main/java/org/wso2/carbon/certificate/mgt/cert/jaxrs/api/impl/CertificateManagementAdminServiceImpl.java

@@ -121,9 +121,13 @@ public class CertificateManagementAdminServiceImpl implements CertificateManagem
 
         CertificateManagementService certificateService = DeviceMgtAPIUtils.getCertificateManagementService();
         try {
-            certificateService.removeCertificate(serialNumber);
+            boolean status = certificateService.removeCertificate(serialNumber);
+            if (!status) {
+                Response.status(Response.Status.NOT_FOUND).entity("No certificate is found with the given " +
+                        "serial number '" + serialNumber + "'");
+            }
             return Response.status(Response.Status.OK).entity("Certificate that carries the serial number '" +
-                    serialNumber + " has been removed").build();
+                    serialNumber + "' has been removed").build();
         } catch (CertificateManagementDAOException e) {
             String msg = "Error occurred while converting PEM file to X509Certificate";
             log.error(msg, e);

components/certificate-mgt/org.wso2.carbon.certificate.mgt.core/src/main/java/org/wso2/carbon/certificate/mgt/core/dao/impl/GenericCertificateDAOImpl.java

@@ -252,10 +252,7 @@ public class GenericCertificateDAOImpl implements CertificateDAO {
             stmt.setString(1, serialNumber);
             stmt.setInt(2, tenantId);
 
-            if(stmt.executeUpdate() > 0) {
-                return true;
-            }
-            return false;
+            return stmt.executeUpdate() > 0;
         } catch (SQLException e) {
             String errorMsg =
                     "Unable to get the read the certificate with serial" + serialNumber;

components/certificate-mgt/org.wso2.carbon.certificate.mgt.core/src/main/java/org/wso2/carbon/certificate/mgt/core/service/CertificateManagementServiceImpl.java

@@ -173,7 +173,7 @@ public class CertificateManagementServiceImpl implements CertificateManagementSe
         try {
             CertificateManagementDAOFactory.beginTransaction();
             CertificateDAO certificateDAO = CertificateManagementDAOFactory.getCertificateDAO();
-            Boolean status = certificateDAO.removeCertificate(serialNumber);
+            boolean status = certificateDAO.removeCertificate(serialNumber);
             CertificateManagementDAOFactory.commitTransaction();
             return status;
         } catch (TransactionManagementException e) {