public Builder putUserEnvVars(java.lang.String key, java.lang.String value) {
      if (key == null) {
        throw new NullPointerException("map key");
      }
      if (value == null) {
        throw new NullPointerException("map value");
      }
      internalGetMutableUserEnvVars().getMutableMap().put(key, value);
      bitField0_ |= 0x00002000;
      return this;
    }
<pre>
Optional. User-defined environment variables associated with this workflow
revision. This map has a maximum length of 20. Each string can take up to
4KiB. Keys cannot be empty strings and cannot start with "GOOGLE" or
"WORKFLOWS".
</pre>

<code>map&lt;string, string&gt; user_env_vars = 14 [(.google.api.field_behavior) = OPTIONAL];
</code>
java-workflows/proto-google-cloud-workflows-v1/src/main/java/com/google/cloud/workflows/v1/Workflow.java