code: public boolean isExtensionEnabled(String extensionName) {
          Boolean state = extensionsState.get(extensionName);
          if (state == null) {
              return true;
          }
          return state;
      }
docs: Tells whether or not the extension with the given name is enabled.
  <p>
  Extensions are enabled by default.
  
  @param extensionName the name of the extension to check.
  @return {@code true} if extension is enabled, {@code false} otherwise.
  @since 2.6.0
  @see #getExtensionsState()