Adding more context to exception message

Author: ssambasu

marklogic-data-hub/src/main/java/com/marklogic/hub/step/impl/WriteStepRunner.java

@@ -308,7 +308,7 @@ public RunStepResponse run() {
             }
             if(fileLocations.get("separator") != null) {
                 if(! this.inputFileType.equalsIgnoreCase("csv")){
-                    throw new IllegalArgumentException("Invalid argument for file type " + inputFileType );
+                    throw new IllegalArgumentException("Invalid argument for file type " + inputFileType + ". When specifying a separator, the file type must be 'csv'");
                 }
                 this.separator = fileLocations.get("separator").trim();
                 if (separator.equals("\\t")) {

ml-data-hub-plugin/src/main/groovy/com/marklogic/gradle/task/RunFlowTask.groovy

@@ -187,7 +187,7 @@ class RunFlowTask extends HubTask {
             }
             if(separator != null) {
                 if(inputFileType != null && !inputFileType.equalsIgnoreCase("csv")) {
-                    throw new IllegalArgumentException("Invalid argument for file type " + inputFileType)
+                    throw new IllegalArgumentException("Invalid argument for file type " + inputFileType + ". When specifying a separator, the file type must be 'csv'")
                 }
                 runFlowString.append("\n\t\tSeparator:" + separator.toString())
                 fileLocations.put("separator", separator)