bugfix: 修复api创建任务时，表格使用默认值导致渲染失败的问题

pipeline_plugins/variables/collections/datatable.py

@@ -10,12 +10,11 @@
 an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
 specific language governing permissions and limitations under the License.
 """
-
+import json
 import logging
 
 from django.conf import settings
 from django.utils.translation import ugettext_lazy as _
-
 from pipeline.core.data.var import LazyVariable
 from pipeline.core.flow.io import StringItemSchema
 
@@ -24,6 +23,14 @@
 
 class DataTableValue(object):
     def __init__(self, data):
+        try:
+            # data 为 字符串的情况下表示可能使用了默认值，
+            # 尝试序列化，不然下面也会报错
+            if isinstance(data, str):
+                data = json.loads(data)
+        except Exception as e:
+            logger.exception("[datatable] value error, value = {}, error={}".format(data, e))
+
         self._value = data
         item_values = {}
         for item in data: