How to access a field in Child Pipe Line

Hi,
when I am trying to access Col Desc field in child pipe line getting the below error
sample JSON
{
“Style”:“Pen”,
“Col Desc”: “Black”
}

“failure”: “Validation errors:\nproperty_map.settings.transformations.value.mappingTable.value[4].expression.value: Expression parsing failed near – _content). >> [ << 'Çol Desc (Reason: Mismatched input ‘[’ at line 1:21. Expecting one of: {, ‘||’, ‘&&’, ‘^’, ‘==’, ‘!=’, ‘>’, ‘<’, ‘>=’, ‘<=’, ‘+’, ‘-’, ‘*’, ‘/’, ‘%’, ‘?’, ‘instanceof’, ‘in’, ‘matches’}; Resolution: Please check expression syntax)\n”,