Fxed an element duplication error

src/system_utils/DataStore.java

@@ -1351,6 +1351,7 @@ public boolean import_element_choices(String file_path) {
 		    	String[] elem_and_elems = line.split(":");
 		    	Element main_elem = Element.valueOf(elem_and_elems[0]);
 		    	ElementCorrelationInfo eci = correlations.get(main_elem);
+		    	eci.clear_selection();
 		    	for (String s : elem_and_elems[1].split(",")) {
 		    		eci.add_selected(Element.valueOf(s));
 		    	}

src/system_utils/ElementCorrelationInfo.java

@@ -318,8 +318,14 @@ public ArrayList<CorrelationInfo> get_selected() {
 	}
 
 	public boolean is_selected(Element secondary) {
-		CorrelationInfo corr = this.all_correlations.get(secondary);
-		return corr.in_use();
+		if (this.all_correlations.containsKey(secondary)) {
+			CorrelationInfo corr = this.all_correlations.get(secondary);
+			if (corr == null) {
+				return false;
+			}
+			return corr.in_use();
+		}
+		return false;
 	}
 
 	// These set methods are used by datastore to pass along changes
@@ -338,6 +344,16 @@ public void remove_selected(Element secondary) {
 		this.selected_elements.remove(corr);
 	}
 
+	public void clear_selection() {
+		for (Element e : Element.values()) {
+			if (is_selected(e)) {
+
+				remove_selected(e);
+
+			}
+		}
+	}
+
 	public ArrayList<Element> get_selected_names() {
 		ArrayList<Element> sel = new ArrayList<Element>();
 		for (CorrelationInfo corr : get_selected()) {