missing the character '+' in my response

I am using the soapui5.2 and found when my response has a character '+' inside, it will be deleted automatically when response.

for example. my response should be like below 

{
"op": "core/text-transform",
"description": "[Remove Characters Before 'formation)'] [CutBefore]",
"engineConfig": {
"facets": [],
"mode": "row-based"
},
"columnName": "CutBefore",
"expression": "grel:trim(if(isBlank(partition(value, 'formation)')[1]), value, partition(value, 'formation)')[1] + partition(value, 'formation)')[2]))",
"onError": "keep-original",
"repeat": false,
"repeatCount": 10
}

however, the response show up in soapui at expression has changed to 

"expression": "grel:trim(if(isBlank(partition(value, 'formation)')[1]), value, partition(value, 'formation)')[1] partition(value, 'formation)')[2]))",

the '+' is missing. this made my next post fail.Does anyone meet this problem? is there any solution? thanks for help