Fix incorrect argument to Checker Framework, and fix nullness warnings. (#1354)

709d97aa321d5729988fd63b960bbece04cfba10 modified the -AskipDefs argument to the
Checker Framework (a regular expression) in a way that caused it to skip
checking all files.  This commit fixes the regular expression and the new
Checker Framework warnings.

2 files changed, 4 insertions, 2 deletions

diff --git a/api/src/main/java/io/opencensus/common/ServerStatsFieldEnums.java b/api/src/main/java/io/opencensus/common/ServerStatsFieldEnums.java
index 92194d96..79cb196e 100644
--- a/api/src/main/java/io/opencensus/common/ServerStatsFieldEnums.java
+++ b/api/src/main/java/io/opencensus/common/ServerStatsFieldEnums.java
@@ -17,6 +17,7 @@
 package io.opencensus.common;
 
 import java.util.TreeMap;
+import javax.annotation.Nullable;
 
 /**
  * A Enum representation for Ids and Size for attributes of {@code ServerStats}.
@@ -85,8 +86,9 @@ public final class ServerStatsFieldEnums {
      * @return the numerical value of the id. null if the id is not valid
      * @since 0.16
      */
+    @Nullable
     public static Id valueOf(int value) {
-      return (Id) map.get(value);
+      return map.get(value);
     }
   }
 
diff --git a/api/src/main/java/io/opencensus/trace/SpanBuilder.java b/api/src/main/java/io/opencensus/trace/SpanBuilder.java
index 00e11572..1a4e29e9 100644
--- a/api/src/main/java/io/opencensus/trace/SpanBuilder.java
+++ b/api/src/main/java/io/opencensus/trace/SpanBuilder.java
@@ -335,7 +335,7 @@ public abstract class SpanBuilder {
     }
 
     @Override
-    public SpanBuilder setSpanKind(Span.Kind spanKind) {
+    public SpanBuilder setSpanKind(@Nullable Span.Kind spanKind) {
       return this;
     }