private com.google.protobuf.MapField<java.lang.String, java.lang.String>
        internalGetMutableHeaders() {
      if (headers_ == null) {
        headers_ = com.google.protobuf.MapField.newMapField(HeadersDefaultEntryHolder.defaultEntry);
      }
      if (!headers_.isMutable()) {
        headers_ = headers_.copy();
      }
      bitField0_ |= 0x00000008;
      onChanged();
      return headers_;
    }
<pre>
The relative URL.

The relative URL must begin with "/" and must be a valid HTTP relative URL.
It can contain a path and query string arguments.
If the relative URL is empty, then the root path "/" will be used.
No spaces are allowed, and the maximum length allowed is 2083 characters.
</pre>

<code>string relative_url = 3;</code>

@param value The bytes for relativeUrl to set.
@return This builder for chaining.
java-tasks/proto-google-cloud-tasks-v2beta2/src/main/java/com/google/cloud/tasks/v2beta2/AppEngineHttpRequest.java