Fix bug.

lib/tasks/exec_command.rake

@@ -197,10 +197,12 @@ namespace :exec_commands do
               if data.include?("\n") || outputs.empty?
                 output_lines = data_str.split("\n")
                 first_output = output_lines[0]
-                if outputs.count != 0
-                  outputs[-1] += first_output
-                else
-                  outputs << first_output
+                if first_output
+                  if outputs.count != 0
+                    outputs[-1] += first_output
+                  else
+                    outputs << first_output
+                  end
                 end
                 new_arr = output_lines[1..-1]
                 if data_str[-1] == "\n"