chore: add isUndefined assertion

---
type: pre_commit_static_analysis_report
description: Results of running static analysis checks when committing changes.
report:
  - task: lint_filenames
    status: passed
  - task: lint_editorconfig
    status: passed
  - task: lint_markdown
    status: na
  - task: lint_package_json
    status: na
  - task: lint_repl_help
    status: na
  - task: lint_javascript_src
    status: passed
  - task: lint_javascript_cli
    status: na
  - task: lint_javascript_examples
    status: na
  - task: lint_javascript_tests
    status: na
  - task: lint_javascript_benchmarks
    status: na
  - task: lint_python
    status: na
  - task: lint_r
    status: na
  - task: lint_c_src
    status: na
  - task: lint_c_examples
    status: na
  - task: lint_c_benchmarks
    status: na
  - task: lint_c_tests_fixtures
    status: na
  - task: lint_shell
    status: na
  - task: lint_typescript_declarations
    status: passed
  - task: lint_typescript_tests
    status: na
  - task: lint_license_headers
    status: passed
---

Author: Sachinn-64

lib/node_modules/@stdlib/plot/vega/mark/symbol/lib/size/set.js

@@ -24,6 +24,7 @@
 
 var logger = require( 'debug' );
 var isNonNegativeNumber = require( '@stdlib/assert/is-nonnegative-number' ).isPrimitive;
+var isUndefined = require( '@stdlib/assert/is-undefined' );
 var format = require( '@stdlib/string/format' );
 var changeEvent = require( './../change_event.js' );
 var prop = require( './properties.js' );
@@ -39,13 +40,17 @@ var debug = logger( 'vega:symbol-mark:set:'+prop.name );
 /**
 * Sets the symbol size.
 *
+* ## Notes
+*
+* -   Providing `undefined` "unsets" the configured value.
+*
 * @private
 * @param {void|NonNegativeNumber} value - input value
 * @throws {TypeError} must be a nonnegative number
 * @returns {void}
 */
 function set( value ) {
-	if ( !isNonNegativeNumber( value ) ) {
+	if ( !isNonNegativeNumber( value ) && !isUndefined( value ) ) {
 		throw new TypeError( format( 'invalid assignment. `%s` must be a nonnegative number. Value: `%s`.', prop.name, value ) );
 	}
 	if ( value !== this[ prop.private ] ) {