Bug 160184 [API]DataSetID.toString() should return null but return "null"
Description: DataSetID.toString() should return null but return "null" Steps to reproduce: Run below codes: new DataSetID( null, 0, null ).toString(); Expected result: null. Actual result: "null"
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/api/DataSetID.java
StringBuffer buffer = new StringBuffer( );
		append( buffer );
		return buffer.toString( );
	}
	static public DataSetID parse( String dataSetId )
	{
		return parse( dataSetId.toCharArray( ), 0, dataSetId.length( ) );
	}
	static public DataSetID parse( char[] buffer, int offset, int length )
	{
		int ptr = offset + length - 1;
		
		
		
		while ( ptr >= offset && buffer[ptr] != '.' )
		{
			ptr--;
		}
		if ( ptr >= offset && buffer[ptr] == '.' )
		{
			
			
			String queryName = new String( buffer, ptr + 1, offset + length
					- ptr - 1 );
			ptr--; 
			length = ptr - offset + 1;
			
			while ( ptr >= offset && buffer[ptr] != '.' )
			{
				ptr--;