ph-schematron/src/main/java/com/helger/schematron/pure/exchange/PSWriter.java
@Nullable
  public String getXMLStringNotNull (@Nonnull final IPSElement aPSElement)
  {
    final String ret = getXMLString (aPSElement);
    if (ret == null)
      throw new IllegalStateException ("Failed to serialize the passed PS element: " + aPSElement);
    return ret;
  }
@Nullable
  public String getXMLStringNotNull (@Nonnull final IPSElement aPSElement)
  {
    final String ret = getXMLString (aPSElement);
    if (ret == null)
      throw new IllegalStateException ("Failed to serialize the passed PS element: " + aPSElement);
    return ret;
  }
Get the passed Schematron element as a String

@param aPSElement
The schematron element to convert to a string. May not be
<code>null</code>.
@return The passed element as a string and never <code>null</code>.
@throws IllegalStateException
if serialization failed