code: public String getGeometryProperty(TableRef tableRef) {
          TableMapping tableMapping = mappedClasses.get(tableRef);
          if (tableMapping == null) {
              return null;
          }
          for (ColumnMetaData columnMetaData : tableMapping.getMappedColumns()) {
              if (columnMetaData.isGeometry()) {
                  ColumnMapping cm = tableMapping.getColumnMapping(columnMetaData);
                  return cm.getPropertyName();
              }
          }
          return null;
      }
docs: Returns the name of the primary geometry property.
  
  <p>A geometry property is primary when it represents the location and shape of the object.</p>
  
  @param tableRef the <code>TableRef</code> for the table
  @return the name of the primary geometry property, or null if the table specified by the <code>tableRef</code>
  parameter is not mapped or has no primary geometry.
  @throws IllegalStateException if the map() method has not been invoked first.