refactor: allow title text field to be optional

---
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: passed
  - 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: na
  - task: lint_typescript_tests
    status: na
  - task: lint_license_headers
    status: passed
---

Author: kgryte

lib/node_modules/@stdlib/plot/vega/title/lib/main.js

@@ -130,7 +130,7 @@ function transformErrorMessage( msg ) {
 * Title constructor.
 *
 * @constructor
-* @param {Options} options - constructor options
+* @param {Options} [options] - constructor options
 * @param {boolean} [options.aria=true] - boolean indicating whether ARIA attributes should be included in SVG output
 *
 * // FIXME: add parameters
@@ -146,18 +146,22 @@ function transformErrorMessage( msg ) {
 * // returns <Title>
 */
 function Title( options ) {
+	var nargs;
 	var opts;
 	var keys;
 	var v;
 	var k;
 	var i;
+
+	nargs = arguments.length;
 	if ( !( this instanceof Title ) ) {
-		return new Title( options );
+		if ( nargs ) {
+			return new Title( options );
+		}
+		return new Title();
 	}
 	EventEmitter.call( this );
-	if ( !isPlainObject( options ) ) {
-		throw new TypeError( format( 'invalid argument. Options argument must be an object. Value: `%s`.', options ) );
-	}
+
 	// Resolve the default configuration:
 	opts = defaults();
 
@@ -167,24 +171,25 @@ function Title( options ) {
 		k = keys[ i ];
 		this[ '_'+k ] = opts[ k ];
 	}
-	// Check for required properties...
-	if ( !hasProp( options, 'text' ) ) {
-		throw new TypeError( 'invalid argument. Options argument must specify title text.' );
-	}
-	// Validate provided options by attempting to assign option values to corresponding fields...
-	for ( i = 0; i < properties.length; i++ ) {
-		k = properties[ i ];
-		if ( !hasProp( options, k ) ) {
-			continue;
+	if ( nargs ) {
+		if ( !isPlainObject( options ) ) {
+			throw new TypeError( format( 'invalid argument. Options argument must be an object. Value: `%s`.', options ) );
 		}
-		v = options[ k ];
-		try {
-			this[ k ] = v;
-		} catch ( err ) {
-			debug( 'Encountered an error. Error: %s', err.message );
-
-			// FIXME: retain thrown error type
-			throw new Error( transformErrorMessage( err.message ) );
+		// Validate provided options by attempting to assign option values to corresponding fields...
+		for ( i = 0; i < properties.length; i++ ) {
+			k = properties[ i ];
+			if ( !hasProp( options, k ) ) {
+				continue;
+			}
+			v = options[ k ];
+			try {
+				this[ k ] = v;
+			} catch ( err ) {
+				debug( 'Encountered an error. Error: %s', err.message );
+
+				// FIXME: retain thrown error type
+				throw new Error( transformErrorMessage( err.message ) );
+			}
 		}
 	}
 	return this;

lib/node_modules/@stdlib/plot/vega/title/lib/text/set.js

@@ -25,6 +25,7 @@
 var logger = require( 'debug' );
 var isString = require( '@stdlib/assert/is-string' ).isPrimitive;
 var isStringArray = require( '@stdlib/assert/is-string-array' ).primitives;
+var isEmptyArrayLikeObject = require( '@stdlib/assert/is-empty-array-like-object' );
 var hasEqualValues = require( '@stdlib/array/base/assert/has-equal-values' );
 var copy = require( '@stdlib/array/base/copy' );
 var join = require( '@stdlib/array/base/join' );
@@ -48,7 +49,7 @@ var debug = logger( 'vega:title:set:text' );
 */
 function set( value ) {
 	var isStr = isString( value );
-	if ( !isStr && !isStringArray( value ) ) {
+	if ( !isStr && !isStringArray( value ) && !isEmptyArrayLikeObject( value ) ) { // eslint-disable-line max-len
 		throw new TypeError( format( 'invalid assignment. `%s` must be a string or an array of strings. Value: `%s`.', 'text', value ) );
 	}
 	if ( isStr ) {

lib/node_modules/@stdlib/plot/vega/visualization/examples/index.js

@@ -27,9 +27,7 @@ var Visualization = require( './../lib' );
 
 var autosize = new Autosize();
 var padding = new Padding();
-var title = new Title({
-	'text': 'Hello World!'
-});
+var title = new Title();
 var xScale = new LinearScale({
 	'name': 'xScale',
 	'domain': [ 0, 99 ],