fix(metrics): Do not flush when no metrics were added to avoid printing root-level _aws dict.

Author: phipag

powertools-metrics/src/main/java/software/amazon/lambda/powertools/metrics/internal/EmfMetricsLogger.java

@@ -164,8 +164,9 @@ public void flush() {
             } else {
                 LOGGER.warn("No metrics were emitted");
             }
+        } else {
+            emfLogger.flush();
         }
-        emfLogger.flush();
     }
 
     @Override

powertools-metrics/src/test/java/software/amazon/lambda/powertools/metrics/internal/EmfMetricsLoggerTest.java

@@ -348,6 +348,8 @@ void shouldLogWarningOnEmptyMetrics() throws Exception {
         // Read the log file and check for the warning
         String logContent = new String(Files.readAllBytes(logFile.toPath()), StandardCharsets.UTF_8);
         assertThat(logContent).contains("No metrics were emitted");
+        // No EMF output should be generated
+        assertThat(outputStreamCaptor.toString().trim()).isEmpty();
     }
 
     @Test