code: @Override
      public String permissionsToString() {
          if (this.permissions == null) {
              return Constants.EMPTY_STRING;
          }
  
          // The service supports a fixed order => rcwdl
          final StringBuilder builder = new StringBuilder();
  
          if (this.permissions.contains(SharedAccessFilePermissions.READ)) {
              builder.append("r");
          }
  
          if (this.permissions.contains(SharedAccessFilePermissions.CREATE)) {
              builder.append("c");
          }
  
          if (this.permissions.contains(SharedAccessFilePermissions.WRITE)) {
              builder.append("w");
          }
  
          if (this.permissions.contains(SharedAccessFilePermissions.DELETE)) {
              builder.append("d");
          }
  
          if (this.permissions.contains(SharedAccessFilePermissions.LIST)) {
              builder.append("l");
          }
  
          return builder.toString();
      }
docs: Converts this policy's permissions to a string.
  
  @return A <code>String</code> that represents the shared access permissions in the "rcwdl" format,
  which is described at {@link #setPermissionsFromString(String)}.