code: public Schema from(String originFieldName) {
  		if (lastField == null) {
  			throw new ValidationException("No field previously defined. Use field() before.");
  		}
  		tableSchema.get(lastField).put(SCHEMA_FROM, originFieldName);
  		lastField = null;
  		return this;
  	}
docs: Specifies the origin of the previously defined field. The origin field is defined by a
  connector or format.
  
  <p>E.g. field("myString", Types.STRING).from("CSV_MY_STRING")
  
  <p>Note: Field names are matched by the exact name by default (case sensitive).