How to get meta data from a document set using script snap?

I want to get the meta data of a document using a script snap.i prepared the below javascript using script snap. Its working fine at validation time but failing at runtime.
please find my script below.

// Ensure compatibility with both JDK 7 and 8 JSR-223 Script Engines
try { load("nashorn:mozilla_compat.js"); } catch(e) { }

// Import the interface required by the Script snap.
importPackage(com.snaplogic.scripting.language);

// Import the Java utility classes.
importPackage(java.util);

/**
 * Create an object that implements the methods defined by the "ScriptHook"
 * interface.  We'll be passing this object to the constructor for the
 * ScriptHook interface.
 */
var impl = {
    /*
     * These variables (input, output, error, log) are defined by the
     * ExecuteScript snap when evaluating this script.
     */
    input : input,
    output : output,
    error : error,
    log : log,

    /**
     * The "execute()" method is called once when the pipeline is started
     * and allowed to process its inputs or just send data to its outputs.
     *
     * Exceptions are automatically caught and sent to the error view.
     */
    execute : function () {
       this.log.info("Executing Transform Script");
      // var i=0;
        if (this.input.hasNext() ) {
            try{
                // Read the next document, wrap it in a map and write out the wrapper
                
                var doc = this.input.next();
                 var keyArray = doc.keySet().toArray();
                  var wrapperOut ={};
                 for( var index in keyArray) 
                        {
                             var new_data = {};
                            var key = keyArray[index];
                            var type=(!isNaN(parseInt(doc.get(key))) ? 'int' : 'binary');
                           //  wrapperOut.put("data_type",type);
                           //  wrapperOut.put("col_name",key);
                           wrapperOut.data_type=type;
                           wrapperOut.col_name=key;
                          output.write(wrapperOut);
                          //  wrapperOut.add(new_data);
                            
                        }
               
             //   wrapper.put("original", doc);
              //  
                this.log.info("Transform Script finished");
               
               
            }
            catch(err) {
                var wrapper = new java.util.HashMap();
                wrapper.put("errorMsg", err);
                this.log.error(err);
                this.error.write(wrapper);
            }
           // i++;
        }
      //  output.write(wrapperOut);
        this.log.info(" data"+wrapperOut.toString());
       // this.output.write(doc, wrapperOut);
    }
};

/**
 * The Script Snap will look for a ScriptHook object in the "hook"
 * variable.  The snap will then call the hook's "execute" method.
 */
var hook = new com.snaplogic.scripting.language.ScriptHook(impl);

Where is wrong with this script?Its failing at runtime giving below error:
java.io.IOException: Failed to close subscriber

If the document view is:
items color price

car red 1100
mango green 5

Then my desired output is:
column name type

items string
color string
price int