src/main/java/org/jboss/util/propertyeditor/PropertyEditors.java
public static final boolean isNull(final String value, final boolean trim, final boolean empty)
   {
      // For backwards compatibility
      if (disableIsNull)
         return false;
      // No value?
      if (value == null)
         return true;
      // Trim the text when requested
      String trimmed = trim ? value.trim() : value;
      // Is the empty string null?
      if (empty && trimmed.length() == 0)
         return true;
      // Just check it.
      return NULL.equalsIgnoreCase(trimmed);
   }
public static final boolean isNull(final String value, final boolean trim, final boolean empty)
   {
      // For backwards compatibility
      if (disableIsNull)
         return false;
      // No value?
      if (value == null)
         return true;
      // Trim the text when requested
      String trimmed = trim ? value.trim() : value;
      // Is the empty string null?
      if (empty && trimmed.length() == 0)
         return true;
      // Just check it.
      return NULL.equalsIgnoreCase(trimmed);
   }
Whether a string is interpreted as the null value

@param value the value
@param trim whether to trim the string
@param empty whether to include the empty string as null
@return true when the string has the value null