public Builder mergeStringValue(com.google.devtools.cloudtrace.v2.TruncatableString value) {
      if (stringValueBuilder_ == null) {
        if (valueCase_ == 1
            && value_ != com.google.devtools.cloudtrace.v2.TruncatableString.getDefaultInstance()) {
          value_ =
              com.google.devtools.cloudtrace.v2.TruncatableString.newBuilder(
                      (com.google.devtools.cloudtrace.v2.TruncatableString) value_)
                  .mergeFrom(value)
                  .buildPartial();
        } else {
          value_ = value;
        }
        onChanged();
      } else {
        if (valueCase_ == 1) {
          stringValueBuilder_.mergeFrom(value);
        } else {
          stringValueBuilder_.setMessage(value);
        }
      }
      valueCase_ = 1;
      return this;
    }
<pre>
A string up to 256 bytes long.
</pre>

<code>.google.devtools.cloudtrace.v2.TruncatableString string_value = 1;</code>
java-trace/proto-google-cloud-trace-v2/src/main/java/com/google/devtools/cloudtrace/v2/AttributeValue.java