Fixed crash executing ""

src/main/java/com/mojang/brigadier/CommandDispatcher.java

@@ -39,9 +39,13 @@ public class CommandDispatcher<S> {
         root.addChild(command.build());
     }
 
-    public int execute(String command, S source) throws CommandException {
+    public int execute(String input, S source) throws CommandException {
-        CommandContext<S> context = parse(command, source).build();
+        CommandContext<S> context = parse(input, source).build();
-        return context.getCommand().run(context);
+        Command<S> command = context.getCommand();
+        if (command == null) {
+            throw ERROR_UNKNOWN_COMMAND.create();
+        }
+        return command.run(context);
     }
 
     public CommandContextBuilder<S> parse(String command, S source) throws CommandException {

src/test/java/com/mojang/brigadier/CommandDispatcherTest.java

@@ -117,6 +117,19 @@ public class CommandDispatcherTest {
         }
     }
 
+    @Test
+    public void testExecuteEmptyCommand() throws Exception {
+        subject.register(literal(""));
+
+        try {
+            subject.execute("", source);
+            fail();
+        } catch (CommandException ex) {
+            assertThat(ex.getType(), is(CommandDispatcher.ERROR_UNKNOWN_COMMAND));
+            assertThat(ex.getData(), is(Collections.<String, Object>emptyMap()));
+        }
+    }
+
     @Test
     public void testExecuteUnknownSubcommand() throws Exception {
         subject.register(literal("foo").executes(command));