diff -u b/src/Plugin/paragraphs/Behavior/ParagraphsStylePlugin.php b/src/Plugin/paragraphs/Behavior/ParagraphsStylePlugin.php
--- b/src/Plugin/paragraphs/Behavior/ParagraphsStylePlugin.php
+++ b/src/Plugin/paragraphs/Behavior/ParagraphsStylePlugin.php
@@ -261,7 +261,7 @@
     // In case the current style is not set, fallback to the default style.
     // If default style is set to none, no style will be applied.
     $paragraph_styles = [];
-    if (isset($this->configuration['defaults'])) {
+    if (!empty($this->configuration['defaults'])) {
       foreach ($this->configuration['defaults'] as $key => $value) {
         $paragraph_styles[$key] = $paragraph->getBehaviorSetting($this->getPluginId(), $key, $this->configuration['defaults'][$key]);
       }
diff -u b/src/Tests/ParagraphsStylePluginTest.php b/src/Tests/ParagraphsStylePluginTest.php
--- b/src/Tests/ParagraphsStylePluginTest.php
+++ b/src/Tests/ParagraphsStylePluginTest.php
@@ -322,7 +322,7 @@
   }
 
   /**
-   * Tests the style selection plugin settings and functionality.
+   * Tests the multiple style selection plugin settings and functionality.
    */
   public function testMultipleGroups() {
     // Install Paragraph Collection Test in order to have styles.
@@ -340,35 +340,6 @@
     $this->addParagraphsType($paragraph_type);
     // Add a text field.
     $this->fieldUIAddExistingField('admin/structure/paragraphs_type/' . $paragraph_type, 'paragraphs_text', $paragraph_type);
-    $this->drupalGet('admin/structure/paragraphs_type/' . $paragraph_type);
-    $this->assertFieldByName('behavior_plugins[style][settings][groups][]');
-    $this->assertFieldByName('behavior_plugins[style][settings][default]', '');
-    $edit = [
-      'behavior_plugins[style][enabled]' => TRUE,
-      'behavior_plugins[style][settings][groups][]' => [],
-      'behavior_plugins[style][settings][default]' => '',
-    ];
-    $this->drupalPostForm(NULL, $edit, t('Save'));
-
-    // Create paragraphed content.
-    $this->drupalGet('node/add/paragraphed_test');
-    $this->drupalPostAjaxForm(NULL, [], 'paragraphs_test_style_plugin_add_more');
-
-    // Check that a style without a style group is available.
-    $options = $this->xpath('//select[@name=:name]//option[normalize-space(text())=:text]', [
-      ':name' => 'paragraphs[0][behavior_plugins][style][style_wrapper][style]',
-      ':text' => 'Groupless',
-    ]);
-    $this->assertTrue(isset($options[0]), 'Groupless style available.');
-
-    // Check that the style options are sorted alphabetically.
-    $styles = $this->xpath('//select[contains(@id, :id)]', [':id' => 'edit-paragraphs-0-behavior-plugins-style-style']);
-    $this->assertEqual('- Default -', $styles[0]->option[0]);
-    $this->assertEqual('Bold', $styles[0]->option[1]);
-    $this->assertEqual('Groupless', $styles[0]->option[2]);
-    $this->assertEqual('Italic', $styles[0]->option[3]);
-    $this->assertEqual('Regular', $styles[0]->option[4]);
-    $this->assertEqual('Underline', $styles[0]->option[5]);
 
     // Restrict the paragraphs type to the "Italic Test Group" style group.
     $this->drupalGet('admin/structure/paragraphs_type/' . $paragraph_type);
@@ -382,10 +353,7 @@
       'behavior_plugins[style][settings][defaults][italic_test_group]' => 'italic',
     ];
     $this->drupalPostForm(NULL, $edit, t('Save'));
-
-    $this->drupalGet('admin/structure/paragraphs_type/' . $paragraph_type);
-
-    // Check that the style without a style group is no longer available.
+    // Create a paragraphed test node and check the style classes.
     $this->drupalGet('node/add/paragraphed_test');
     $this->drupalPostAjaxForm(NULL, [], 'paragraphs_test_style_plugin_add_more');
     // Since Italic Group defines only two styles, assert that only they appear.
@@ -400,7 +368,7 @@
     $this->drupalPostForm(NULL, $edit, 'Save');
     $this->assertRaw('paragraphs-behavior-style--italic');
 
-    // Configure Regular as a default style.
+    // Configure two groups and set their defaults.
     $this->drupalGet('admin/structure/paragraphs_type/' . $paragraph_type);
     $edit = [
       'behavior_plugins[style][settings][groups][]' => ['Italic Test Group', 'Regular Test Group'],
@@ -409,12 +377,12 @@
     $edit = [
       'behavior_plugins[style][settings][groups][]' => ['Italic Test Group', 'Regular Test Group'],
       'behavior_plugins[style][settings][defaults][regular_test_group]' => 'regular',
+      'behavior_plugins[style][settings][defaults][italic_test_group]' => 'italic',
     ];
     $this->drupalPostForm(NULL, $edit, t('Save'));
-
+    // Check the selects elements for each enabled group and check the classes.
     $node = $this->getNodeByTitle('title_to_remember');
     $this->drupalGet('node/' . $node->id() . '/edit');
-    // Since Italic Group defines only two styles, assert that only they appear.
     $styles = $this->xpath('//select[contains(@name, :name)]', [':name' => 'paragraphs[0][behavior_plugins][style][style_wrapper][regular_test_group]']);
     $this->assertEqual(2, count($styles[0]->option));
     $this->assertEqual('- Regular -', $styles[0]->option[0]);
@@ -423,26 +391,100 @@
     $this->assertEqual(2, count($styles[0]->option));
     $this->assertEqual('- Italic -', $styles[0]->option[0]);
     $this->assertEqual('Bold', $styles[0]->option[1]);
+    $this->drupalGet('node/' . $node->id());
+    $this->assertRaw('paragraphs-behavior-style--italic');
+    $this->assertRaw('paragraphs-behavior-style--regular');
+
+    // Configure Regular as a default style.
+    $this->drupalGet('admin/structure/paragraphs_type/' . $paragraph_type);
+    $edit = [
+      'behavior_plugins[style][settings][groups][]' => ['Regular Test Group'],
+    ];
+    $this->drupalPostAjaxForm(NULL, $edit, 'behavior_plugins[style][settings][groups][]');
     $edit = [
-      'paragraphs[0][behavior_plugins][style][style_wrapper][italic_test_group]' => 'bold',
+      'behavior_plugins[style][settings][groups][]' => ['Regular Test Group'],
+      'behavior_plugins[style][settings][defaults][regular_test_group]' => 'bold',
     ];
     $this->drupalPostForm(NULL, $edit, t('Save'));
+    // Check that there is only one select and only one style class.
+    $this->drupalGet('node/' . $node->id() . '/edit');
+    $styles = $this->xpath('//select[contains(@name, :name)]', [':name' => 'paragraphs[0][behavior_plugins][style][style_wrapper][regular_test_group]']);
+    $this->assertEqual(2, count($styles[0]->option));
+    $this->assertEqual('- Bold -', $styles[0]->option[0]);
+    $this->assertEqual('Regular', $styles[0]->option[1]);
+    $styles = $this->xpath('//select[contains(@name, :name)]', [':name' => 'paragraphs[0][behavior_plugins][style][style_wrapper][italic_test_group]']);
+    $this->assertEqual([], $styles);
+    $this->drupalGet('node/' . $node->id());
+    $this->assertNoRaw('paragraphs-behavior-style--italic');
+    $this->assertRaw('paragraphs-behavior-style--bold');
 
+    // Configure Regular as a default style.
+    $this->drupalGet('admin/structure/paragraphs_type/' . $paragraph_type);
+    $edit = [
+      'behavior_plugins[style][settings][groups][]' => ['Italic Test Group', 'Regular Test Group', 'Underline Test Group'],
+    ];
+    $this->drupalPostAjaxForm(NULL, $edit, 'behavior_plugins[style][settings][groups][]');
+    $edit = [
+      'behavior_plugins[style][settings][groups][]' => ['Italic Test Group', 'Regular Test Group', 'Underline Test Group'],
+      'behavior_plugins[style][settings][defaults][italic_test_group]' => 'italic',
+      'behavior_plugins[style][settings][defaults][regular_test_group]' => 'regular',
+      'behavior_plugins[style][settings][defaults][underline_test_group]' => 'underline',
+    ];
+    $this->drupalPostForm(NULL, $edit, t('Save'));
+    // Check that there is only one select and only one style class.
+    $this->drupalGet('node/' . $node->id() . '/edit');
+    $styles = $this->xpath('//select[contains(@name, :name)]', [':name' => 'paragraphs[0][behavior_plugins][style][style_wrapper][regular_test_group]']);
+    $this->assertEqual(2, count($styles[0]->option));
+    $this->assertEqual('- Regular -', $styles[0]->option[0]);
+    $this->assertEqual('Bold', $styles[0]->option[1]);
+    $styles = $this->xpath('//select[contains(@name, :name)]', [':name' => 'paragraphs[0][behavior_plugins][style][style_wrapper][italic_test_group]']);
+    $this->assertEqual(2, count($styles[0]->option));
+    $this->assertEqual('- Italic -', $styles[0]->option[0]);
+    $this->assertEqual('Bold', $styles[0]->option[1]);
+    $styles = $this->xpath('//select[contains(@name, :name)]', [':name' => 'paragraphs[0][behavior_plugins][style][style_wrapper][underline_test_group]']);
+    $this->assertEqual(2, count($styles[0]->option));
+    $this->assertEqual('- Underline -', $styles[0]->option[0]);
+    $this->assertEqual('Bold', $styles[0]->option[1]);
     $this->drupalGet('node/' . $node->id());
+    $this->assertRaw('paragraphs-behavior-style--italic');
     $this->assertRaw('paragraphs-behavior-style--regular');
+    $this->assertRaw('paragraphs-behavior-style--underline');
+
+    // Change a plugin.
+    $this->drupalGet('node/' . $node->id() . '/edit');
+    $edit = [
+      'paragraphs[0][behavior_plugins][style][style_wrapper][regular_test_group]' => 'bold'
+    ];
+    $this->drupalPostForm(NULL, $edit, 'Save');
+    $this->assertRaw('paragraphs-behavior-style--italic');
     $this->assertRaw('paragraphs-behavior-style--bold');
+    $this->assertRaw('paragraphs-behavior-style--underline');
 
-    // Configure Regular as a default style.
+    // Configure no groups.
     $this->drupalGet('admin/structure/paragraphs_type/' . $paragraph_type);
     $edit = [
-      'behavior_plugins[style][settings][groups][]' => ['Regular Test Group'],
+      'behavior_plugins[style][settings][groups][]' => [],
     ];
     $this->drupalPostAjaxForm(NULL, $edit, 'behavior_plugins[style][settings][groups][]');
     $edit = [
-      'behavior_plugins[style][settings][groups][]' => ['Regular Test Group'],
-      'behavior_plugins[style][settings][defaults][regular_test_group]' => 'bold',
+      'behavior_plugins[style][settings][groups][]' => [],
     ];
     $this->drupalPostForm(NULL, $edit, t('Save'));
+    // Check that there is only one select and only one style class.
+    $this->drupalGet('node/' . $node->id() . '/edit');
+    $styles = $this->xpath('//select[contains(@name, :name)]', [':name' => 'paragraphs[0][behavior_plugins][style][style_wrapper][regular_test_group]']);
+    $this->assertEqual([], $styles);
+    $styles = $this->xpath('//select[contains(@name, :name)]', [':name' => 'paragraphs[0][behavior_plugins][style][style_wrapper][italic_test_group]']);
+    $this->assertEqual([], $styles);
+    $styles = $this->xpath('//select[contains(@name, :name)]', [':name' => 'paragraphs[0][behavior_plugins][style][style_wrapper][underline_test_group]']);
+    $this->assertEqual([], $styles);
+    $edit = [
+      'paragraphs[0][behavior_plugins][style][style_wrapper][style]' => 'underline'
+    ];
+    $this->drupalPostForm(NULL, $edit, 'Save');
+    $this->assertNoRaw('paragraphs-behavior-style--italic');
+    $this->assertNoRaw('paragraphs-behavior-style--bold');
+    $this->assertRaw('paragraphs-behavior-style--underline');
   }
 
 }