Don't crash on empty tracestate value (#3104)

api/all/src/main/java/io/opentelemetry/api/trace/ArrayBasedTraceStateBuilder.java

@@ -5,6 +5,7 @@
 
 package io.opentelemetry.api.trace;
 
+import io.opentelemetry.api.internal.StringUtils;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
@@ -158,7 +159,7 @@ final class ArrayBasedTraceStateBuilder implements TraceStateBuilder {
   // Value is opaque string up to 256 characters printable ASCII RFC0020 characters (i.e., the range
   // 0x20 to 0x7E) except comma , and =.
   private static boolean isValueValid(@Nullable String value) {
-    if (value == null) {
+    if (StringUtils.isNullOrEmpty(value)) {
       return false;
     }
     if (value.length() > VALUE_MAX_SIZE || value.charAt(value.length() - 1) == ' ' /* '\u0020' */) {

api/all/src/test/java/io/opentelemetry/api/trace/propagation/W3CTraceContextPropagatorTest.java

@@ -436,6 +436,24 @@ class W3CTraceContextPropagatorTest {
                 TRACE_ID_BASE16, SPAN_ID_BASE16, TraceFlags.getSampled(), TraceState.getDefault()));
   }
 
+  @Test
+  void extract_InvalidTracestate_EmptyValue() {
+    Map<String, String> invalidHeaders = new HashMap<>();
+    invalidHeaders.put(
+        W3CTraceContextPropagator.TRACE_PARENT,
+        "00-" + TRACE_ID_BASE16 + "-" + SPAN_ID_BASE16 + "-01");
+    invalidHeaders.put(W3CTraceContextPropagator.TRACE_STATE, "foo=,test=test");
+    assertThat(
+            getSpanContext(
+                w3cTraceContextPropagator.extract(Context.current(), invalidHeaders, getter)))
+        .isEqualTo(
+            SpanContext.createFromRemoteParent(
+                TRACE_ID_BASE16,
+                SPAN_ID_BASE16,
+                TraceFlags.getSampled(),
+                TraceState.builder().put("test", "test").build()));
+  }
+
   @Test
   void extract_InvalidTracestate_OneString() {
     Map<String, String> invalidHeaders = new HashMap<>();