Get rid of dependency on Guava

Since I789f9aa589 removed usage of Guava's Optional, we only have
the dependency on Guava for the following simple utility methods:

  Strings.isNullOrEmpty
  MoreObjects.firstNonNull

Remove the dependency and instead provide own implementations
of those methods.

Change-Id: Iddcc20005004d37dae703fc0522c546a5212575c

lib/BUCK

diff --git a/lib/BUCK b/lib/BUCK
index 9c596fa..d333cba 100644
--- a/lib/BUCK
+++ b/lib/BUCK
@@ -1,13 +1,6 @@
 include_defs('//bucklets/maven_jar.bucklet')
 
 maven_jar(
-  name = 'guava',
-  id = 'com.google.guava:guava:19.0-rc2',
-  sha1 = '93e17f60bc524c2610b41c494bb829c11ca89436',
-  license = 'Apache2.0',
-)
-
-maven_jar(
   name = 'junit',
   id = 'junit:junit:4.11',
   sha1 = '4e031bb61df09069aeb2bffb4019e7a5034a4ee0',
@@ -20,7 +13,6 @@
   sha1 = 'bd17774d2dc0fffa884d42c07d2537e86c67acd6',
   license = 'DO_NOT_DISTRIBUTE',
   exported_deps = [
-    ':guava',
     ':junit',
   ],
 )

src/main/java/com/googlesource/gerrit/plugins/cookbook/HelloProjectAction.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/cookbook/HelloProjectAction.java b/src/main/java/com/googlesource/gerrit/plugins/cookbook/HelloProjectAction.java
index 8057bb7..0e5f6f0 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/cookbook/HelloProjectAction.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/cookbook/HelloProjectAction.java
@@ -14,8 +14,6 @@
 
 package com.googlesource.gerrit.plugins.cookbook;
 
-import com.google.common.base.MoreObjects;
-import com.google.common.base.Strings;
 import com.google.gerrit.extensions.restapi.RestModifyView;
 import com.google.gerrit.extensions.webui.UiAction;
 import com.google.gerrit.server.CurrentUser;
@@ -39,6 +37,20 @@
     this.user = user;
   }
 
+  private boolean isNullOrEmpty(String s) {
+    return s == null || s.isEmpty();
+  }
+
+  private Object firstNonNull(String first, String second) {
+    if (first != null) {
+      return first;
+    }
+    if (second != null) {
+      return second;
+    }
+    throw new NullPointerException();
+  }
+
   @Override
   public String apply(ProjectResource rsrc, Input input) {
     final String greeting = input.french
@@ -46,8 +58,8 @@
         : "Hello";
     return String.format("%s %s from project %s!",
         greeting,
-        Strings.isNullOrEmpty(input.message)
-            ? MoreObjects.firstNonNull(user.get().getUserName(), "world")
+        isNullOrEmpty(input.message)
+            ? firstNonNull(user.get().getUserName(), "world")
             : input.message,
         rsrc.getName());
   }