title: How to pass the dynamic fieldName in filter condition of dataweave mule
body: <p>I have data in cache i.e objectstore. I need to get the data from cache and apply the filter condition on it.</p>
  
  <p>Here requirement is, I have to expose api to get the data based on filedName and filedValue which will come dynamically in the request. </p>
  
  <p>sample request :</p>
  
  <pre><code>https://localhost:8082/api/customer/filter?fieldName=customerId&amp;fieldValue=101810
  </code></pre>
  
  <p>I have return code to filter the data in dataweave but it is not working. can you please help on this</p>
  
  <pre><code>%dw 1.0
  %output application/json
  ---
  payload.rows filter (("$.content." ++ flowVars.fieldName ++ ".content") as :string == flowVars.fieldValue as :string) map ((row , indexOfRow) -&gt; {
      customerId: row.content.customerId.content as :string when row.content.customerId.content != null otherwise null,
      customerName: row.content.customerName.content as :string when row.content.customerName.content != null otherwise null,
      customerAddress:row.content.customerAddress.content as :string when row.content.customerAddress.content != null otherwise null
  })
  </code></pre>
  
  <p>and I am getting below error</p>
  
  <pre><code>Exception while executing: 
  payload.rows filter (("$.content." ++ flowVars.fieldName ++ ".content") as :string == flowVars.fieldValue as :string) map ((row , indexOfRow) -&gt; {
                        ^
  Type mismatch for '++' operator
       found :object, :string
    required :string, :string.
  </code></pre>
  
  <p>can you please help on this</p>