Fix #1426 Error saving any dynamic network in gexf format

modules/ExportPlugin/src/main/java/org/gephi/io/exporter/plugin/ExporterGEXF.java

@@ -382,7 +382,8 @@ public class ExporterGEXF implements GraphExporter, CharacterExporter, LongTask
                 if (timeMap != null) {
                     for (Interval interval : timeMap.toKeysArray()) {
                         if (!exportVisible || interval.compareTo(visibleInterval) == 0) {
-                            Object value = timeMap.get(interval, null);
+                            final Object defaultValue = null;
+                            final Object value = timeMap.get(interval, defaultValue);
                             if (value != null) {
                                 xmlWriter.writeStartElement(ATTVALUE);
                                 xmlWriter.writeAttribute(ATTVALUE_FOR, column.getId());
@@ -405,7 +406,8 @@ public class ExporterGEXF implements GraphExporter, CharacterExporter, LongTask
                 if (timeMap != null) {
                     for (Double timestamp : timeMap.toKeysArray()) {
                         if (!exportVisible || visibleInterval.compareTo(timestamp) == 0) {
-                            Object value = timeMap.get(timestamp, null);
+                            final Object defaultValue = null;
+                            final Object value = timeMap.get(timestamp, defaultValue);
                             if (value != null) {
                                 xmlWriter.writeStartElement(ATTVALUE);
                                 xmlWriter.writeAttribute(ATTVALUE_FOR, column.getId());

modules/ExportPlugin/src/main/nbm/manifest.mf

 Manifest-Version: 1.0
 AutoUpdate-Essential-Module: true
 OpenIDE-Module-Localizing-Bundle: org/gephi/io/exporter/plugin/Bundle.properties
-OpenIDE-Module-Specification-Version: 0.9.1.1
+OpenIDE-Module-Specification-Version: 0.9.1.2
 OpenIDE-Module-Display-Category: Plugin
 OpenIDE-Module-Name: Export Plugin