A conditional dataset must contain at least one branching condition and exactly one fallback/default case, both of which must refer to existing datasets. 

{
  "name": "CustomerNames",
  "type": "Conditional",
  "conditions": [
      { "if": "$[Type] == 1 && !startsWith($[CustomerName], \"Test\")", "then": "FullNames" },
      { "otherwise": "CompanyNames" }
  ]
}