public Builder mergeFunctionName(com.google.devtools.cloudtrace.v2.TruncatableString value) {
        if (functionNameBuilder_ == null) {
          if (((bitField0_ & 0x00000001) != 0)
              && functionName_ != null
              && functionName_
                  != com.google.devtools.cloudtrace.v2.TruncatableString.getDefaultInstance()) {
            getFunctionNameBuilder().mergeFrom(value);
          } else {
            functionName_ = value;
          }
        } else {
          functionNameBuilder_.mergeFrom(value);
        }
        if (functionName_ != null) {
          bitField0_ |= 0x00000001;
          onChanged();
        }
        return this;
      }
<pre>
The fully-qualified name that uniquely identifies the function or
method that is active in this frame (up to 1024 bytes).
</pre>

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