Validate dataschema datasource (#5785)

* Validate dataschema has a datasource

* Fix tests

* Use Guava Strings.isNullOrEmpty

* Inverse nullempty check, whoops

server/src/main/java/io/druid/segment/indexing/DataSchema.java

@@ -25,6 +25,7 @@ import com.fasterxml.jackson.annotation.JsonIgnore;
 import com.fasterxml.jackson.annotation.JsonProperty;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.google.common.base.Preconditions;
+import com.google.common.base.Strings;
 import com.google.common.collect.Sets;
 import io.druid.data.input.impl.DimensionsSpec;
 import io.druid.data.input.impl.InputRowParser;
@@ -68,10 +69,12 @@ public class DataSchema
   )
   {
     this.jsonMapper = Preconditions.checkNotNull(jsonMapper, "null ObjectMapper.");
-    this.dataSource = Preconditions.checkNotNull(dataSource, "dataSource cannot be null. Please provide a dataSource.");
     this.parser = parser;
     this.transformSpec = transformSpec == null ? TransformSpec.NONE : transformSpec;
 
+    Preconditions.checkArgument(!Strings.isNullOrEmpty(dataSource), "dataSource cannot be null or empty. Please provide a dataSource.");
+    this.dataSource = dataSource;
+
     if (granularitySpec == null) {
       log.warn("No granularitySpec has been specified. Using UniformGranularitySpec as default.");
       this.granularitySpec = new UniformGranularitySpec(null, null, null);

server/src/test/java/io/druid/segment/indexing/DataSchemaTest.java

@@ -285,6 +285,43 @@ public class DataSchemaTest
     // Jackson creates a default type parser (StringInputRowParser) for an invalid type.
     schema.getParser();
   }
+  
+  @Test
+  public void testEmptyDatasource() throws Exception
+  {
+    Map<String, Object> parser = jsonMapper.convertValue(
+        new StringInputRowParser(
+            new JSONParseSpec(
+                new TimestampSpec("time", "auto", null),
+                new DimensionsSpec(
+                    DimensionsSpec.getDefaultSchemas(ImmutableList.of("time", "dimA", "dimB", "col2")),
+                    ImmutableList.of("dimC"),
+                    null
+                ),
+                null,
+                null
+            ),
+            null
+        ), JacksonUtils.TYPE_REFERENCE_MAP_STRING_OBJECT
+    );
+
+    expectedException.expect(CoreMatchers.instanceOf(IllegalArgumentException.class));
+    expectedException.expectMessage(
+        "dataSource cannot be null or empty. Please provide a dataSource."
+    );
+
+    DataSchema schema = new DataSchema(
+        "",
+        parser,
+        new AggregatorFactory[]{
+            new DoubleSumAggregatorFactory("metric1", "col1"),
+            new DoubleSumAggregatorFactory("metric2", "col2"),
+            },
+        new ArbitraryGranularitySpec(Granularities.DAY, ImmutableList.of(Intervals.of("2014/2015"))),
+        null,
+        jsonMapper
+    );
+  }
 
   @Test
   public void testSerde() throws Exception