code: public Schema field(String fieldName, String fieldType) {
  		if (tableSchema.containsKey(fieldName)) {
  			throw new ValidationException("Duplicate field name $fieldName.");
  		}
  
  		LinkedHashMap<String, String> fieldProperties = new LinkedHashMap<>();
  		fieldProperties.put(SCHEMA_TYPE, fieldType);
  
  		tableSchema.put(fieldName, fieldProperties);
  
  		lastField = fieldName;
  		return this;
  	}
docs: Adds a field with the field name and the type string. Required.
  This method can be called multiple times. The call order of this method defines
  also the order of the fields in a row.
  
  @param fieldName the field name
  @param fieldType the type string of the field