NullPointerException when an external JDBC driver returns null instead of the ResultSetMetaData instance

[AnastasiiaSergienko]

Problem

We don't check if the metadata of the result set is present. So the method mapResultMetadataToExasolDataTypes of the ResultSetMetadataReader throws a null pointer exception when the ResultSetMetaData is null. This happened in the Sybase dialect.

Solution

We want to validate the metadata and throw a dedicated exception if it's null.

[AnastasiiaSergienko]

Logs:

2021-05-11 14:35:58.898 FINER   [c.e.a.d.AbstractQueryRewriter] Push-down query generated with SybaseSqlGenerationVisitor:
SELECT TOP 1000 * FROM [master].[monCachePool]
2021-05-11 14:35:58.901 FINE    [c.e.a.j.ResultSetMetadataReader] Generating columns description for push-down query using BaseColumnMetadataReader:
SELECT TOP 1000 * FROM [master].[monCachePool]
2021-05-11 14:35:58.909 SEVERE  [c.e.a.RequestDispatcher] null
2021-05-11 14:35:58.910 FINE    [c.e.a.RequestDispatcher] Stack trace:
	java.lang.NullPointerException
	at com.exasol.adapter.jdbc.ResultSetMetadataReader.mapResultMetadataToExasolDataTypes(ResultSetMetadataReader.java:91)
	at com.exasol.adapter.jdbc.ResultSetMetadataReader.describeColumns(ResultSetMetadataReader.java:44)
	at com.exasol.adapter.dialects.ImportIntoQueryRewriter.createImportColumnsDescription(ImportIntoQueryRewriter.java:40)
	at com.exasol.adapter.dialects.ImportIntoQueryRewriter.generateImportStatement(ImportIntoQueryRewriter.java:31)
	at com.exasol.adapter.dialects.AbstractQueryRewriter.rewrite(AbstractQueryRewriter.java:52)
	at com.exasol.adapter.dialects.AbstractSqlDialect.rewriteQuery(AbstractSqlDialect.java:134)
	at com.exasol.adapter.jdbc.JdbcAdapter.pushdown(JdbcAdapter.java:210)
	at com.exasol.adapter.RequestDispatcher.dispatchPushDownRequestToAdapter(RequestDispatcher.java:142)
	at com.exasol.adapter.RequestDispatcher.processRequest(RequestDispatcher.java:80)
	at com.exasol.adapter.RequestDispatcher.executeAdapterCall(RequestDispatcher.java:52)
	at com.exasol.adapter.RequestDispatcher.adapterCall(RequestDispatcher.java:41)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.base/java.lang.reflect.Method.invoke(Method.java:566)
	at com.exasol.ExaWrapper.runSingleCall(ExaWrapper.java:100)