|  | @@ -66,7 +66,7 @@ var path = require('path'),
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				|  |  |   * amber_dir: points to the location of an amber installation
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				|  |  |   */
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				|  |  |  function AmberCompiler(amber_dir) {
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				|  |  | -    if (undefined === amber_dir || !fs.existsSync(amber_dir)) {
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				|  |  | +    if (amber_dir == null || !fs.existsSync(amber_dir)) {
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				|  |  |          throw new Error('amber_dir needs to be a valid directory');
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				|  |  |      }
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				|  |  |  
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				|  | @@ -111,7 +111,7 @@ AmberCompiler.prototype.main = function (configuration, finished_callback) {
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				|  |  |          configuration.amd_namespace = 'amber_core';
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				|  |  |      }
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				|  |  |  
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				|  |  | -    if (undefined !== configuration.jsLibraryDirs) {
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				|  |  | +    if (configuration.jsLibraryDirs != null) {
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				|  |  |          configuration.jsLibraryDirs.push(path.join(this.amber_dir, 'src'));
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				|  |  |          configuration.jsLibraryDirs.push(path.join(this.amber_dir, 'support'));
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				|  |  |      }
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				|  | @@ -154,7 +154,7 @@ AmberCompiler.prototype.main = function (configuration, finished_callback) {
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				|  |  |   */
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				|  |  |  function check_configuration(configuration) {
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				|  |  |      return new Promise(function (resolve, reject) {
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				|  |  | -        if (undefined === configuration) {
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				|  |  | +        if (configuration == null) {
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				|  |  |              reject(Error('AmberCompiler.check_configuration_ok(): missing configuration object'));
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				|  |  |          }
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				|  |  |  
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				|  | @@ -439,7 +439,7 @@ function category_export(configuration) {
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				|  |  |              return new Promise(function (resolve, reject) {
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				|  |  |                  var category = path.basename(stFile, '.st');
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				|  |  |                  var jsFilePath = configuration.output_dir;
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				|  |  | -                if (undefined === jsFilePath) {
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				|  |  | +                if (jsFilePath == null) {
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				|  |  |                      jsFilePath = path.dirname(stFile);
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				|  |  |                  }
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				|  |  |                  var jsFile = category + '.js';
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