Add more null annotations (issue #359).

This commit adds some Nullable annotations that are required by the Checker
Framework, but it doesn't change any other code.  It also suppresses some Error
Prone and FindBugs warnings that conflict with the Checker Framework, since the
three tools use different algorithms.

6 files changed, 13 insertions, 7 deletions

diff --git a/api/src/main/java/io/opencensus/tags/TagContext.java b/api/src/main/java/io/opencensus/tags/TagContext.java
index 8147906b..13fde2ac 100644
--- a/api/src/main/java/io/opencensus/tags/TagContext.java
+++ b/api/src/main/java/io/opencensus/tags/TagContext.java
@@ -21,6 +21,7 @@ import com.google.common.collect.ImmutableMultiset;
 import com.google.common.collect.Lists;
 import com.google.common.collect.Multiset;
 import java.util.Iterator;
+import javax.annotation.Nullable;
 import javax.annotation.concurrent.Immutable;
 
 /**
@@ -59,7 +60,7 @@ public abstract class TagContext {
    * performance.
    */
   @Override
-  public boolean equals(Object other) {
+  public boolean equals(@Nullable Object other) {
     if (!(other instanceof TagContext)) {
       return false;
     }
diff --git a/api/src/main/java/io/opencensus/trace/SpanContext.java b/api/src/main/java/io/opencensus/trace/SpanContext.java
index 5e88b9fd..6084c674 100644
--- a/api/src/main/java/io/opencensus/trace/SpanContext.java
+++ b/api/src/main/java/io/opencensus/trace/SpanContext.java
@@ -18,6 +18,7 @@ package io.opencensus.trace;
 
 import com.google.common.base.MoreObjects;
 import com.google.common.base.Objects;
+import javax.annotation.Nullable;
 import javax.annotation.concurrent.Immutable;
 
 /**
@@ -85,7 +86,7 @@ public final class SpanContext {
   }
 
   @Override
-  public boolean equals(Object obj) {
+  public boolean equals(@Nullable Object obj) {
     if (obj == this) {
       return true;
     }
diff --git a/api/src/main/java/io/opencensus/trace/SpanId.java b/api/src/main/java/io/opencensus/trace/SpanId.java
index cf0c7d46..76747acf 100644
--- a/api/src/main/java/io/opencensus/trace/SpanId.java
+++ b/api/src/main/java/io/opencensus/trace/SpanId.java
@@ -23,6 +23,7 @@ import com.google.common.base.MoreObjects;
 import com.google.common.io.BaseEncoding;
 import java.util.Arrays;
 import java.util.Random;
+import javax.annotation.Nullable;
 import javax.annotation.concurrent.Immutable;
 
 /**
@@ -162,7 +163,7 @@ public final class SpanId implements Comparable<SpanId> {
   }
 
   @Override
-  public boolean equals(Object obj) {
+  public boolean equals(@Nullable Object obj) {
     if (obj == this) {
       return true;
     }
diff --git a/api/src/main/java/io/opencensus/trace/Status.java b/api/src/main/java/io/opencensus/trace/Status.java
index f34ab693..d5807ef5 100644
--- a/api/src/main/java/io/opencensus/trace/Status.java
+++ b/api/src/main/java/io/opencensus/trace/Status.java
@@ -249,8 +249,9 @@ public final class Status {
 
   // The canonical code of this message.
   private final CanonicalCode canonicalCode;
+
   // An additional error message.
-  private final String description;
+  @Nullable private final String description;
 
   private Status(CanonicalCode canonicalCode, @Nullable String description) {
     this.canonicalCode = checkNotNull(canonicalCode, "canonicalCode");
@@ -304,7 +305,7 @@ public final class Status {
    * additional fields may be added to Status in the future.
    */
   @Override
-  public boolean equals(Object obj) {
+  public boolean equals(@Nullable Object obj) {
     if (obj == this) {
       return true;
     }
diff --git a/api/src/main/java/io/opencensus/trace/TraceId.java b/api/src/main/java/io/opencensus/trace/TraceId.java
index 20f81393..2fad8949 100644
--- a/api/src/main/java/io/opencensus/trace/TraceId.java
+++ b/api/src/main/java/io/opencensus/trace/TraceId.java
@@ -24,6 +24,7 @@ import com.google.common.io.BaseEncoding;
 import io.opencensus.common.Internal;
 import java.util.Arrays;
 import java.util.Random;
+import javax.annotation.Nullable;
 import javax.annotation.concurrent.Immutable;
 
 /**
@@ -184,7 +185,7 @@ public final class TraceId implements Comparable<TraceId> {
   }
 
   @Override
-  public boolean equals(Object obj) {
+  public boolean equals(@Nullable Object obj) {
     if (obj == this) {
       return true;
     }
diff --git a/api/src/main/java/io/opencensus/trace/TraceOptions.java b/api/src/main/java/io/opencensus/trace/TraceOptions.java
index fc594853..2f57f3a7 100644
--- a/api/src/main/java/io/opencensus/trace/TraceOptions.java
+++ b/api/src/main/java/io/opencensus/trace/TraceOptions.java
@@ -23,6 +23,7 @@ import static com.google.common.base.Preconditions.checkNotNull;
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.base.MoreObjects;
 import com.google.common.base.Objects;
+import javax.annotation.Nullable;
 import javax.annotation.concurrent.Immutable;
 
 /**
@@ -150,7 +151,7 @@ public final class TraceOptions {
   }
 
   @Override
-  public boolean equals(Object obj) {
+  public boolean equals(@Nullable Object obj) {
     if (obj == this) {
       return true;
     }