Updated main sparkApplication to avoid to require master variable

dhp-common/src/main/scala/eu/dnetlib/dhp/application/SparkScalaApplication.scala

@@ -65,12 +65,13 @@ abstract class AbstractScalaApplication(
     val conf: SparkConf = new SparkConf()
     val master = parser.get("master")
     log.info(s"Creating Spark session: Master: $master")
-    SparkSession
+    val b = SparkSession
       .builder()
       .config(conf)
       .appName(getClass.getSimpleName)
-      .master(master)
-      .getOrCreate()
+    if (master != null)
+      b.master(master)
+    b.getOrCreate()
   }
 
   def reportTotalSize(targetPath: String, outputBasePath: String): Unit = {

dhp-workflows/dhp-graph-mapper/src/main/resources/eu/dnetlib/dhp/sx/create_scholix_dump_params.json

@@ -1,5 +1,5 @@
 [
-  {"paramName":"mt",  "paramLongName":"master",     "paramDescription": "should be local or yarn",  "paramRequired": true},
+  {"paramName":"mt",  "paramLongName":"master",     "paramDescription": "should be local or yarn",  "paramRequired": false},
   {"paramName":"s",   "paramLongName":"sourcePath", "paramDescription": "the source Path",           "paramRequired": true},
   {"paramName":"t",   "paramLongName":"targetPath", "paramDescription": "the path of the scholix dump", "paramRequired": true}
 ]