03babf928b4b69bce4c86dcf5d0abab9a435e336
max
  Mon May 15 13:08:09 2017 -0700
fixing strange error when showing only 0 or 1 gene in hgGeneGraph, refs #18626

diff --git src/hg/hgGeneGraph/hgGeneGraph src/hg/hgGeneGraph/hgGeneGraph
index 8b39204..6164183 100755
--- src/hg/hgGeneGraph/hgGeneGraph
+++ src/hg/hgGeneGraph/hgGeneGraph
@@ -509,30 +509,33 @@
         # no filtering
         return links
 
     # filter links
     filtLinks = {}
     for pair, pairData in links.iteritems():
         docCount, dbList, tagSet = pairData[:3]
         if len(showTags.intersection(tagSet))!=0:
             filtLinks[pair] = pairData
     return filtLinks
 
 def buildGraph(conn, gene, geneCount, minSupp, addNeighbors):
     """ get (gene,gene) links from database and annotate with weights and tags
     only get links with minSupp articles for each link  
     """
+    if geneCount <= 1:
+        errAbort("Sorry, you have to show at least two genes.")
+
     links = queryLinks(conn, gene=gene)
 
     if len(links)==0:
         errAbort("Sorry, the gene %s is not a valid gene symbol or is not present in any gene interaction database." % cgi.escape(gene))
 
     links = filterLinks(links)
 
     lowLinks = defaultdict(set)
     graphLinks, lowLinks = splitHighLowLinks(links, gene, minSupp, lowLinks, geneCount)
 
     if addNeighbors:
         # create the links between all other genes, be less stringent about these
         otherGenes = set()
         for genes, pmids in graphLinks.iteritems():
             otherGenes.update(genes)