diff --git a/src/main/java/org/gcube/common/workspacetaskexecutor/dataminer/WorkspaceDataMinerTaskExecutor.java b/src/main/java/org/gcube/common/workspacetaskexecutor/dataminer/WorkspaceDataMinerTaskExecutor.java
index 1162ced..dc5ec9a 100644
--- a/src/main/java/org/gcube/common/workspacetaskexecutor/dataminer/WorkspaceDataMinerTaskExecutor.java
+++ b/src/main/java/org/gcube/common/workspacetaskexecutor/dataminer/WorkspaceDataMinerTaskExecutor.java
@@ -1,6 +1,7 @@
 package org.gcube.common.workspacetaskexecutor.dataminer;
 
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.List;
 
 import org.apache.commons.lang.Validate;
@@ -449,7 +450,6 @@ public class WorkspaceDataMinerTaskExecutor implements ExecutableTask<TaskConfig
 	 * @throws Exception the exception
 	 */
 	public List<TaskOperator> getListOperators(String[] filterForParameterTypes, FilterOperator operator) throws Exception{
-		logger.info("Getting list operators applying filters: "+filterForParameterTypes+", operator: "+operator);
 
 		DataMinerAccessPoint dap = getDataMinerAccessPoint();
 
@@ -458,6 +458,11 @@ public class WorkspaceDataMinerTaskExecutor implements ExecutableTask<TaskConfig
 			return dap.getListOperators();
 		}
 
+		List<String> listFilterParameterTypes = new ArrayList<String>();
+		listFilterParameterTypes.addAll(Arrays.asList(filterForParameterTypes));
+		listFilterParameterTypes.removeAll(Arrays.asList("", null));
+		logger.info("Getting list operators applying filters: "+listFilterParameterTypes+", operator: "+operator);
+
 		List<TaskOperator> filteredListOperators = new ArrayList<TaskOperator>(dap.getListOperators().size());
 
 		if(operator==null){
@@ -471,25 +476,39 @@ public class WorkspaceDataMinerTaskExecutor implements ExecutableTask<TaskConfig
 			List<TaskParameter> io = taskOperator.getInputOperators();
 			int filterPassed = 0;
 
+			List<String> matchedFilter = new ArrayList<String>();
 			for (TaskParameter taskParameter : io) {
-				logger.trace("key: "+taskParameter.getKey() + ", value: "+taskParameter.getValue() +", defaultValue: "+taskParameter.getDefaultValue());
-				for (String filterParameterName : filterForParameterTypes) {
-					if(taskParameter.getType().getType().compareToIgnoreCase(filterParameterName)==0){
-						filterPassed++;
+				logger.trace("has type: "+taskParameter.getType());
+				for (String filterParameterName : listFilterParameterTypes) {
+					if(taskParameter.getType()!=null){
+						if(taskParameter.getType().getType().compareToIgnoreCase(filterParameterName)==0){
+							//IGNORING FILTER ALREADY MATCHED
+							if(!matchedFilter.contains(filterParameterName)){
+								matchedFilter.add(filterParameterName);
+								filterPassed++;
+							}
+						}
 					}
 				}
 			}
 
 			if(operator.equals(FilterOperator.LOGICAL_OR) && filterPassed>=1){
 				filteredListOperators.add(taskOperator);
-				logger.debug("Added operator: "+taskOperator + " It is matching "+FilterOperator.LOGICAL_OR +" and filterPassed>=1");
+				logger.info("Added operator: "+taskOperator.getName() + " It is matching "+FilterOperator.LOGICAL_OR +" with filters: "+listFilterParameterTypes);
+				logger.trace("Operators are: "+taskOperator.getInputOperators());
 			//IN AND ALL FILTERS MUST BE MATCHED
-			}else if(operator.equals(FilterOperator.LOGICAL_AND) && filterPassed==filterForParameterTypes.length){
+			}else if(operator.equals(FilterOperator.LOGICAL_AND) && filterPassed==listFilterParameterTypes.size()){
 				filteredListOperators.add(taskOperator);
-				logger.debug("Added operator: "+taskOperator + " It is matching "+FilterOperator.LOGICAL_AND +" and filterPassed==filterForParameterNames.length");
+				logger.info("Added operator: "+taskOperator.getName()+ " It is matching "+FilterOperator.LOGICAL_AND +" with filters: "+listFilterParameterTypes);
+				logger.trace("Operators are: "+taskOperator.getInputOperators());
 			}
-			else{
-				logger.info("Removed operator: "+taskOperator + " It does not match the filters: "+filterForParameterTypes);
+			else if(operator.equals(FilterOperator.LOGICAL_NOT) && filterPassed==0){
+				filteredListOperators.add(taskOperator);
+				logger.info("Added operator: "+taskOperator.getName() + " It is matching "+FilterOperator.LOGICAL_NOT +" with filters: "+listFilterParameterTypes);
+				logger.trace("Operators are: "+taskOperator.getInputOperators());
+			}else{
+				logger.info("Removed operator: "+taskOperator.getName() + " It is not matching the operator: "+operator+" with filters: "+listFilterParameterTypes);
+				logger.trace("Operators are: "+taskOperator.getInputOperators());
 				filteredListOperators.remove(taskOperator);
 			}
 
diff --git a/src/main/java/org/gcube/common/workspacetaskexecutor/shared/FilterOperator.java b/src/main/java/org/gcube/common/workspacetaskexecutor/shared/FilterOperator.java
index 788c1ab..762d9e9 100644
--- a/src/main/java/org/gcube/common/workspacetaskexecutor/shared/FilterOperator.java
+++ b/src/main/java/org/gcube/common/workspacetaskexecutor/shared/FilterOperator.java
@@ -15,5 +15,6 @@ import java.io.Serializable;
 public enum FilterOperator implements Serializable{
 
 	LOGICAL_OR,
-	LOGICAL_AND;
+	LOGICAL_AND,
+	LOGICAL_NOT;
 }