private com.google.protobuf.SingleFieldBuilderV3<
            com.google.devtools.cloudtrace.v2.TruncatableString,
            com.google.devtools.cloudtrace.v2.TruncatableString.Builder,
            com.google.devtools.cloudtrace.v2.TruncatableStringOrBuilder>
        getStringValueFieldBuilder() {
      if (stringValueBuilder_ == null) {
        if (!(valueCase_ == 1)) {
          value_ = com.google.devtools.cloudtrace.v2.TruncatableString.getDefaultInstance();
        }
        stringValueBuilder_ =
            new com.google.protobuf.SingleFieldBuilderV3<
                com.google.devtools.cloudtrace.v2.TruncatableString,
                com.google.devtools.cloudtrace.v2.TruncatableString.Builder,
                com.google.devtools.cloudtrace.v2.TruncatableStringOrBuilder>(
                (com.google.devtools.cloudtrace.v2.TruncatableString) value_,
                getParentForChildren(),
                isClean());
        value_ = null;
      }
      valueCase_ = 1;
      onChanged();
      return stringValueBuilder_;
    }
<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