Check for null in more public methods in Span and its subclasses.

Author: sebright2

api/src/main/java/io/opencensus/trace/BlankSpan.java

@@ -91,7 +91,9 @@ public void setStatus(Status status) {
 
   /** No-op implementation of the {@link Span#end(EndSpanOptions)} method. */
   @Override
-  public void end(EndSpanOptions options) {}
+  public void end(EndSpanOptions options) {
+    Utils.checkNotNull(options, "options");
+  }
 
   @Override
   public String toString() {

api/src/test/java/io/opencensus/trace/NoopSpan.java

@@ -30,7 +30,7 @@ public class NoopSpan extends Span {
 
   /** Creates a new {@code NoopSpan}. */
   public NoopSpan(SpanContext context, @Nullable EnumSet<Options> options) {
-    super(context, options);
+    super(Utils.checkNotNull(context, "context"), options);
   }
 
   @Override
@@ -63,5 +63,7 @@ public void addLink(Link link) {
   }
 
   @Override
-  public void end(EndSpanOptions options) {}
+  public void end(EndSpanOptions options) {
+    Utils.checkNotNull(options, "options");
+  }
 }

impl_core/src/main/java/io/opencensus/implcore/trace/SpanImpl.java

@@ -268,6 +268,8 @@ public SpanData toSpanData() {
 
   @Override
   public void putAttribute(String key, AttributeValue value) {
+    Preconditions.checkNotNull(key, "key");
+    Preconditions.checkNotNull(value, "value");
     if (!getOptions().contains(Options.RECORD_EVENTS)) {
       return;
     }
@@ -381,6 +383,7 @@ public void setStatus(Status status) {
 
   @Override
   public void end(EndSpanOptions options) {
+    Preconditions.checkNotNull(options, "options");
     if (!getOptions().contains(Options.RECORD_EVENTS)) {
       return;
     }