post-review changes

Author: SylvainJuge

jmx-scraper/src/main/java/io/opentelemetry/contrib/jmxscraper/JmxScraper.java

@@ -81,10 +81,10 @@ public static void main(String[] args) {
       JmxScraper jmxScraper = new JmxScraper(connectorBuilder, service, scraperConfig);
       jmxScraper.start();
     } catch (ConfigurationException e) {
-      logger.log(Level.SEVERE, "ERROR: invalid configuration ", e);
+      logger.log(Level.SEVERE, "invalid configuration ", e);
       System.exit(1);
     } catch (ArgumentsParsingException e) {
-      logger.log(Level.SEVERE, "ERROR: invalid configuration provided through arguments", e);
+      logger.log(Level.SEVERE, "invalid configuration provided through arguments", e);
       logger.info(
           "Usage: java -jar <path_to_jmxscraper.jar> "
               + "-config <path_to_config.properties or - for stdin>");

jmx-scraper/src/main/java/io/opentelemetry/contrib/jmxscraper/config/JmxScraperConfig.java

@@ -137,9 +137,9 @@ public static JmxScraperConfig fromConfig(ConfigProperties config) {
     scraperConfig.serviceUrl = serviceUrl;
 
     // TODO: we could support multiple values
-    String customConfig = config.getString(JMX_CUSTOM_CONFIG);
+    String customConfig = config.getString(JMX_CUSTOM_CONFIG, "");
     List<String> targetSystem = config.getList(JMX_TARGET_SYSTEM);
-    if (targetSystem.isEmpty() && customConfig == null) {
+    if (targetSystem.isEmpty() && customConfig.isEmpty()) {
       throw new ConfigurationException(
           "at least one of '" + JMX_TARGET_SYSTEM + "' or '" + JMX_CUSTOM_CONFIG + "' must be set");
     }

jmx-scraper/src/main/java/io/opentelemetry/contrib/jmxscraper/config/PropertiesCustomizer.java

@@ -35,7 +35,7 @@ public Map<String, String> apply(ConfigProperties config) {
 
     // providing compatibility with the existing 'otel.jmx.interval.milliseconds' config option
     long intervalLegacy = config.getLong(JMX_INTERVAL_LEGACY, -1);
-    if (config.getDuration(METRIC_EXPORT_INTERVAL) == null && intervalLegacy > 0) {
+    if (config.getDuration(METRIC_EXPORT_INTERVAL) == null && intervalLegacy >= 0) {
       logger.warning(
           METRIC_EXPORT_INTERVAL
               + " deprecated option is used, replacing with '"