made the abstraction more caller friendly

core/src/main/java/hudson/model/AbstractBuild.java

@@ -844,8 +844,8 @@ public abstract class AbstractBuild<P extends AbstractProject<P,R>,R extends Abs
      * @return can be empty list, but never null. Immutable.
      * @since 1.437
      */
-    public List<Environment> getEnvironments() {
-        return buildEnvironments==null ? Collections.<Environment>emptyList() : ImmutableList.copyOf(buildEnvironments);
+    public EnvironmentList getEnvironments() {
+        return new EnvironmentList(buildEnvironments==null ? Collections.<Environment>emptyList() : ImmutableList.copyOf(buildEnvironments));
     }
 
     public Calendar due() {

core/src/main/java/hudson/model/EnvironmentList.java

+/*
+ * The MIT License
+ *
+ * Copyright (c) 2011, CloudBees, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+package hudson.model;
+
+import java.util.AbstractList;
+import java.util.List;
+
+/**
+ * List of {@link Environment}.
+ *
+ * @author Kohsuke Kawaguchi
+ * @since 1.437
+ */
+public final class EnvironmentList extends AbstractList<Environment> {
+    private final List<Environment> base;
+
+    public EnvironmentList(List<Environment> base) {
+        this.base = base;
+    }
+
+    @Override
+    public Environment get(int index) {
+        return base.get(index);
+    }
+
+    @Override
+    public int size() {
+        return base.size();
+    }
+
+    public <T extends Environment> T get(Class<T> type) {
+        for (Environment e : this) {
+            if (type.isInstance(e))
+                return type.cast(e);
+        }
+        return null;
+    }
+}