Fix a GenerateToolUsage issue with no examples

Fixed an issue that would cause the GenerateToolUsage stage of the
build process to fail if it encountered a tool with a null set of
examples.

build-src/toolusage/com/unboundid/buildtools/toolusage/GenerateToolUsage.java

@@ -414,7 +414,7 @@ private static void writeExamples(final PrintWriter w, final String t,
                                     final String s,
                                     final LinkedHashMap<String[],String> m)
   {
-    if (m.isEmpty())
+    if ((m == null) || m.isEmpty())
     {
       return;
     }
@@ -807,7 +807,7 @@ private void printHTMLExamples(final PrintWriter w, final String t,
                                  final String s,
                                  final LinkedHashMap<String[],String> m)
   {
-    if (m.isEmpty())
+    if ((m == null) || m.isEmpty())
     {
       return;
     }