Tolerate empty system options for coverage in Pax-Exam tests

git-svn-id: https://svn.apache.org/repos/asf/sling/trunk@1687546 13f79535-47bb-0310-9956-ffa450edef68
diff --git a/src/test/java/org/apache/sling/commons/log/logback/integration/LogTestBase.java b/src/test/java/org/apache/sling/commons/log/logback/integration/LogTestBase.java
index 6c6cf4d..eed8d5b 100644
--- a/src/test/java/org/apache/sling/commons/log/logback/integration/LogTestBase.java
+++ b/src/test/java/org/apache/sling/commons/log/logback/integration/LogTestBase.java
@@ -112,7 +112,7 @@
 
     private static Option addCodeCoverageOption() {
         String coverageCommand = System.getProperty(COVERAGE_COMMAND);
-        if (coverageCommand != null) {
+        if (coverageCommand != null && !coverageCommand.isEmpty()) {
             return CoreOptions.vmOption(coverageCommand);
         }
         return null;