Use string instead of union of bytes, nullable for message

Author: Sree Raman

kafka-plugins-0.10/widgets/Kafka-batchsource.json

@@ -131,7 +131,7 @@
           "fields": [
             {
               "name": "message",
-              "type": ["bytes", "null"]
+              "type": "string"
             }
           ]
         },

kafka-plugins-0.10/widgets/Kafka-streamingsource.json

@@ -139,7 +139,7 @@
           "fields": [
             {
               "name": "message",
-              "type": ["bytes", "null"]
+              "type": "string"
             }
           ]
         },

kafka-plugins-0.8/widgets/Kafka-batchsource.json

@@ -101,7 +101,7 @@
           "fields": [
             {
               "name": "message",
-              "type": ["bytes", "null"]
+              "type": "string"
             }
           ]
         },

kafka-plugins-0.8/widgets/Kafka-streamingsource.json

@@ -114,7 +114,7 @@
           "fields": [
             {
               "name": "message",
-              "type": ["bytes", "null"]
+              "type": "string"
             }
           ]
         },