When coding against Titan graph database, you may encounter the exception below.

In our case, we are using Tinkerpop Frames, and one frame was using the same value for an edge label as other for a property.

@Adjacency(label="project")

...

@Property("project")

...

To fix that, simply use different values.

Caused by: java.lang.IllegalArgumentException: Querying for edges but including a property key: project
  at com.thinkaurelius.titan.graphdb.query.vertex.BasicVertexCentricQueryBuilder.constructQuery(BasicVertexCentricQueryBuilder.java:428)
  at com.thinkaurelius.titan.graphdb.query.vertex.VertexCentricQueryBuilder.execute(VertexCentricQueryBuilder.java:62)
  at com.thinkaurelius.titan.graphdb.query.vertex.VertexCentricQueryBuilder.titanEdges(VertexCentricQueryBuilder.java:79)
  at com.thinkaurelius.titan.graphdb.query.vertex.VertexCentricQueryBuilder.edges(VertexCentricQueryBuilder.java:98)
  at com.thinkaurelius.titan.graphdb.vertices.AbstractVertex.getEdges(AbstractVertex.java:184)
  at com.tinkerpop.blueprints.util.wrappers.event.EventVertex.getEdges(EventVertex.java:21)
  at com.tinkerpop.frames.annotations.AdjacencyAnnotationHandler.removeEdges(AdjacencyAnnotationHandler.java:100)
  at com.tinkerpop.frames.annotations.AdjacencyAnnotationHandler.processVertex(AdjacencyAnnotationHandler.java:67)
  at com.tinkerpop.frames.annotations.AdjacencyAnnotationHandler.processElement(AdjacencyAnnotationHandler.java:26)
  at com.tinkerpop.frames.annotations.AdjacencyAnnotationHandler.processElement(AdjacencyAnnotationHandler.java:15)
  at com.tinkerpop.frames.FramedElement.invoke(FramedElement.java:140)
  at com.sun.proxy.$Proxy111.setProject(Unknown Source)