Index: trunk/src/org/openstreetmap/josm/command/ChangePropertyCommand.java
===================================================================
--- trunk/src/org/openstreetmap/josm/command/ChangePropertyCommand.java	(revision 15903)
+++ trunk/src/org/openstreetmap/josm/command/ChangePropertyCommand.java	(revision 15905)
@@ -6,8 +6,6 @@
 import static org.openstreetmap.josm.tools.I18n.trn;
 
-import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
-import java.util.HashMap;
 import java.util.LinkedList;
 import java.util.List;
@@ -107,6 +105,5 @@
     public ChangePropertyCommand(Collection<? extends OsmPrimitive> objects, String key, String value) {
         super(objects.iterator().next().getDataSet());
-        this.tags = new HashMap<>(1);
-        this.tags.put(key, value);
+        this.tags = Collections.singletonMap(key, value);
         init(objects);
     }
@@ -121,5 +118,5 @@
      */
     public ChangePropertyCommand(OsmPrimitive object, String key, String value) {
-        this(Arrays.asList(object), key, value);
+        this(Collections.singleton(object), key, value);
     }
 
Index: trunk/src/org/openstreetmap/josm/gui/datatransfer/importers/PrimitiveTagTransferPaster.java
===================================================================
--- trunk/src/org/openstreetmap/josm/gui/datatransfer/importers/PrimitiveTagTransferPaster.java	(revision 15903)
+++ trunk/src/org/openstreetmap/josm/gui/datatransfer/importers/PrimitiveTagTransferPaster.java	(revision 15905)
@@ -7,6 +7,6 @@
 import java.util.Arrays;
 import java.util.Collection;
+import java.util.Collections;
 import java.util.EnumMap;
-import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
@@ -52,6 +52,5 @@
         List<Command> commands = new ArrayList<>();
         for (Tag tag : tagPaster.execute()) {
-            Map<String, String> tags = new HashMap<>(1);
-            tags.put(tag.getKey(), "".equals(tag.getValue()) ? null : tag.getValue());
+            Map<String, String> tags = Collections.singletonMap(tag.getKey(), "".equals(tag.getValue()) ? null : tag.getValue());
             ChangePropertyCommand cmd = new ChangePropertyCommand(OsmDataManager.getInstance().getEditDataSet(), selection, tags);
             if (cmd.getObjectsNumber() > 0) {
Index: trunk/src/org/openstreetmap/josm/io/GeoJSONWriter.java
===================================================================
--- trunk/src/org/openstreetmap/josm/io/GeoJSONWriter.java	(revision 15903)
+++ trunk/src/org/openstreetmap/josm/io/GeoJSONWriter.java	(revision 15905)
@@ -6,5 +6,5 @@
 import java.math.RoundingMode;
 import java.util.Collection;
-import java.util.HashMap;
+import java.util.Collections;
 import java.util.HashSet;
 import java.util.Iterator;
@@ -80,6 +80,5 @@
     public String write(boolean pretty) {
         StringWriter stringWriter = new StringWriter();
-        Map<String, Object> config = new HashMap<>(1);
-        config.put(JsonGenerator.PRETTY_PRINTING, pretty);
+        Map<String, Object> config = Collections.singletonMap(JsonGenerator.PRETTY_PRINTING, pretty);
         try (JsonWriter writer = Json.createWriterFactory(config).createWriter(stringWriter)) {
             JsonObjectBuilder object = Json.createObjectBuilder()