Class Summary does not provide a getter to return inputSchema

In Pig code, https://github.com/apache/pig/blob/trunk/src/org/apache/pig/EvalFunc.java. A private number "inputSchemaInternal" represents the schema. Setter and Getter are also provided
```Java
316 private Schema inputSchemaInternal=null;

328 /**
329 * This method is for internal use. It is called by Pig core in both front-end
330 * and back-end to setup the right input schema for EvalFunc
331 */
332 public void setInputSchema(Schema input){
333 this.inputSchemaInternal=input;
334 }
335
336 /**
337 * This method is intended to be called by the user in {@link EvalFunc} to get the input
338 * schema of the EvalFunc
339 */
340 public Schema getInputSchema(){
341 return this.inputSchemaInternal;
342 }
```

In parquet-mr/parquet-pig/src/main/java/parquet/pig/summary/Summary.java, class Summary extends EvalFunc. It uses a new number called inputSchema(vs. inputSchemaInternal used in class EvalFunc in Pig) to represent schema and override setInputSchema(), but the class does not override getInputSchema() to return inputSchema.

```Java
51 public class Summary extends EvalFunc implements Algebraic {

54 private Schema inputSchema;

257 @Override
258 public void setInputSchema(Schema input) {
259 try {
260 // relation.bag.tuple
261 this.inputSchema=input.getField(0).schema.getField(0).schema;
262 saveSchemaToUDFContext();
263 } catch (FrontendException e) {
264 throw new RuntimeException("Usage: B = FOREACH (GROUP A ALL) GENERATE Summary(A); Can not get schema from " + input, e);
265 } catch (RuntimeException e) {
266 throw new RuntimeException("Usage: B = FOREACH (GROUP A ALL) GENERATE Summary(A); Can not get schema from "+input, e);
267 }
268 }
```

If setInputSchema() of class Summary is called, inputSchema is set. But if we call getInputSchema() afterwards, it will return the value of inputSchemaInternal, which can be still null.

**Reporter**: [Xiang Li](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=xiangli)
#### Related issues:
- [UT TestSummary failed with "java.lang.RuntimeException: Usage: B = FOREACH (GROUP A ALL) GENERATE Summary(A); Can not get schema from null" when Pig >=0.15](https://github.com/apache/parquet-java/issues/1853) (blocks)

_{**Note**: *This issue was originally created as [PARQUET-365](https://issues.apache.org/jira/browse/PARQUET-365). Please see the [migration documentation](https://issues.apache.org/jira/browse/PARQUET-2502) for further details.*}

Beginne in parquet-pig/src/main/java/parquet/pig/summary/Summary.java, indem du das Feld inputSchema und die überschriebene Methode setInputSchema zusammen mit dem Getter von EvalFunc liest. Bestätige den bestehenden Kontext der zugehörigen Tests und stelle dann sicher, dass Aufrufe von getInputSchema das von Summary festgelegte Schema zurückgeben; abgeschlossen ist die Aufgabe, wenn der Getter nicht mehr einen separaten, nicht gesetzten Wert zurückgibt.

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